Many of you have probably seen this already but for those not so fortunate:
http://www.xkcd.com
Here's my favourites so far.
Warning: this comic occasionally contains strong language (which may be unsuitable for children), unusual humor (which may be unsuitable for adults), and advanced mathematics (which may be unsuitable for liberal-arts majors).
http://imgs.xkcd.com/comics/fourier.jpg
http://imgs.xkcd.com/comics/pillar.jpg
http://imgs.xkcd.com/comics/self-reference.jpg
http://imgs.xkcd.com/comics/apple_jacks.jpg
http://imgs.xkcd.com/comics/unspeakable_pun.jpg
http://imgs.xkcd.com/comics/love.jpg
http://imgs.xkcd.com/comics/want.jpg
http://imgs.xkcd.com/comics/science.jpg
http://imgs.xkcd.com/comics/valentine.jpg
http://imgs.xkcd.com/comics/banter.jpg
http://imgs.xkcd.com/comics/pillow_talk.jpg
http://imgs.xkcd.com/comics/cl****.jpg
http://imgs.xkcd.com/comics/familiar.jpg
http://imgs.xkcd.com/comics/garfield.jpg
http://imgs.xkcd.com/comics/attention_shopper.jpg
http://imgs.xkcd.com/comics/katamari.jpg
http://imgs.xkcd.com/comics/so ... osoft_mpaa_riaa_apple.jpg
http://imgs.xkcd.com/comics/gravitational_mass.jpg
http://imgs.xkcd.com/comics/moral_relativity.jpg
http://imgs.xkcd.com/comics/wright_brothers.png
http://imgs.xkcd.com/comics/snakes_on_a_plane_2.jpg
http://imgs.xkcd.com/comics/baring_my_heart.png
http://imgs.xkcd.com/comics/riemann-zeta.jpg
http://imgs.xkcd.com/comics/computational_linguists.png
http://imgs.xkcd.com/comics/pong.png
http://imgs.xkcd.com/comics/centrifugal_force.png
http://imgs.xkcd.com/comics/blogofractal.png
http://imgs.xkcd.com/comics/marketing_interview.png
http://imgs.xkcd.com/comics/dPain_over_dt.png
http://imgs.xkcd.com/comics/music_knowledge.png
http://imgs.xkcd.com/comics/substitute.png
http://imgs.xkcd.com/comics/science_fair.png
http://imgs.xkcd.com/comics/dreams.png
http://imgs.xkcd.com/comics/pointers.png
http://imgs.xkcd.com/comics/delicious.png
http://imgs.xkcd.com/comics/achewood.png
http://imgs.xkcd.com/comics/dinosaur_comics.png
http://imgs.xkcd.com/comics/join_myspace.png
http://imgs.xkcd.com/comics/a_way_so_familiar.png
http://imgs.xkcd.com/comics/search_history.png
http://imgs.xkcd.com/comics/six_months.png
http://imgs.xkcd.com/comics/angular_momentum.jpg
http://imgs.xkcd.com/comics/donald_knuth.png
http://imgs.xkcd.com/comics/global_warming.png
http://imgs.xkcd.com/comics/turn_signals.png
http://imgs.xkcd.com/comics/misusing_slang.png
http://imgs.xkcd.com/comics/reverse_euphemisms.png
http://imgs.xkcd.com/comics/string_theory.png
http://imgs.xkcd.com/comics/skateboarding_is_not_a_crime.png
http://imgs.xkcd.com/comics/automatic_doors.png
http://imgs.xkcd.com/comics/movie_seating.png
http://imgs.xkcd.com/comics/before_sunrise.png
http://imgs.xkcd.com/comics/alice_and_bob.png
http://imgs.xkcd.com/comics/not_really_into_pokemon.png
http://imgs.xkcd.com/comics/e_to_the_pi_times_i.png
http://imgs.xkcd.com/comics/canada.png
http://imgs.xkcd.com/comics/penises.png
http://imgs.xkcd.com/comics/nash.png
http://imgs.xkcd.com/comics/the_familiar.png
http://imgs.xkcd.com/comics/exercise.png
http://imgs.xkcd.com/comics/ipod.png
http://imgs.xkcd.com/comics/working_for_google.png
http://imgs.xkcd.com/comics/the_perfect_sound.png
http://imgs.xkcd.com/comics/map_of_the_internet.jpg
http://imgs.xkcd.com/comics/cat_proximity.png
http://imgs.xkcd.com/comics/color_codes.png
http://imgs.xkcd.com/comics/regular_expressions.png
http://imgs.xkcd.com/comics/command_line_fu.png
http://imgs.xkcd.com/comics/perspective.png
http://imgs.xkcd.com/comics/right_hand_rule.png
http://imgs.xkcd.com/comics/bill_nye.png
http://imgs.xkcd.com/comics/youtube.png
http://imgs.xkcd.com/comics/reno_rhymes.png
http://imgs.xkcd.com/comics/what_xkcd_means.png
http://imgs.xkcd.com/comics/regular_expressions.png
http://imgs.xkcd.com/comics/brain.png
http://imgs.xkcd.com/comics/cat_proximity.png
http://imgs.xkcd.com/comics/the_problem_with_wikipedia.png
http://imgs.xkcd.com/comics/romantic_drama_equation.png
http://imgs.xkcd.com/comics/e_to_the_pi_minus_pi.png
http://imgs.xkcd.com/comics/nintendo_surgeon.png
http://imgs.xkcd.com/comics/blanket_fort.png
http://imgs.xkcd.com/comics/random_number.png
http://imgs.xkcd.com/comics/small_talk.png
http://imgs.xkcd.com/comics/valentines_day.jpg
http://imgs.xkcd.com/comics/lisp.jpg
http://imgs.xkcd.com/comics/open_source.png
http://imgs.xkcd.com/comics/swingset.png
http://imgs.xkcd.com/comics/resonance.png
http://imgs.xkcd.com/comics/graffiti.png
http://imgs.xkcd.com/comics/hamiltonian.png
http://imgs.xkcd.com/comics/collecting_double_takes.png
http://www.xkcd.com
Here's my favourites so far.
Warning: this comic occasionally contains strong language (which may be unsuitable for children), unusual humor (which may be unsuitable for adults), and advanced mathematics (which may be unsuitable for liberal-arts majors).
http://imgs.xkcd.com/comics/fourier.jpg
http://imgs.xkcd.com/comics/pillar.jpg
http://imgs.xkcd.com/comics/self-reference.jpg
http://imgs.xkcd.com/comics/apple_jacks.jpg
http://imgs.xkcd.com/comics/unspeakable_pun.jpg
http://imgs.xkcd.com/comics/love.jpg
http://imgs.xkcd.com/comics/want.jpg
http://imgs.xkcd.com/comics/science.jpg
http://imgs.xkcd.com/comics/valentine.jpg
http://imgs.xkcd.com/comics/banter.jpg
http://imgs.xkcd.com/comics/pillow_talk.jpg
http://imgs.xkcd.com/comics/cl****.jpg
http://imgs.xkcd.com/comics/familiar.jpg
http://imgs.xkcd.com/comics/garfield.jpg
http://imgs.xkcd.com/comics/attention_shopper.jpg
http://imgs.xkcd.com/comics/katamari.jpg
http://imgs.xkcd.com/comics/so ... osoft_mpaa_riaa_apple.jpg
http://imgs.xkcd.com/comics/gravitational_mass.jpg
http://imgs.xkcd.com/comics/moral_relativity.jpg
http://imgs.xkcd.com/comics/wright_brothers.png
http://imgs.xkcd.com/comics/snakes_on_a_plane_2.jpg
http://imgs.xkcd.com/comics/baring_my_heart.png
http://imgs.xkcd.com/comics/riemann-zeta.jpg
http://imgs.xkcd.com/comics/computational_linguists.png
http://imgs.xkcd.com/comics/pong.png
http://imgs.xkcd.com/comics/centrifugal_force.png
http://imgs.xkcd.com/comics/blogofractal.png
http://imgs.xkcd.com/comics/marketing_interview.png
http://imgs.xkcd.com/comics/dPain_over_dt.png
http://imgs.xkcd.com/comics/music_knowledge.png
http://imgs.xkcd.com/comics/substitute.png
http://imgs.xkcd.com/comics/science_fair.png
http://imgs.xkcd.com/comics/dreams.png
http://imgs.xkcd.com/comics/pointers.png
http://imgs.xkcd.com/comics/delicious.png
http://imgs.xkcd.com/comics/achewood.png
http://imgs.xkcd.com/comics/dinosaur_comics.png
http://imgs.xkcd.com/comics/join_myspace.png
http://imgs.xkcd.com/comics/a_way_so_familiar.png
http://imgs.xkcd.com/comics/search_history.png
http://imgs.xkcd.com/comics/six_months.png
http://imgs.xkcd.com/comics/angular_momentum.jpg
http://imgs.xkcd.com/comics/donald_knuth.png
http://imgs.xkcd.com/comics/global_warming.png
http://imgs.xkcd.com/comics/turn_signals.png
http://imgs.xkcd.com/comics/misusing_slang.png
http://imgs.xkcd.com/comics/reverse_euphemisms.png
http://imgs.xkcd.com/comics/string_theory.png
http://imgs.xkcd.com/comics/skateboarding_is_not_a_crime.png
http://imgs.xkcd.com/comics/automatic_doors.png
http://imgs.xkcd.com/comics/movie_seating.png
http://imgs.xkcd.com/comics/before_sunrise.png
http://imgs.xkcd.com/comics/alice_and_bob.png
http://imgs.xkcd.com/comics/not_really_into_pokemon.png
http://imgs.xkcd.com/comics/e_to_the_pi_times_i.png
http://imgs.xkcd.com/comics/canada.png
http://imgs.xkcd.com/comics/penises.png
http://imgs.xkcd.com/comics/nash.png
http://imgs.xkcd.com/comics/the_familiar.png
http://imgs.xkcd.com/comics/exercise.png
http://imgs.xkcd.com/comics/ipod.png
http://imgs.xkcd.com/comics/working_for_google.png
http://imgs.xkcd.com/comics/the_perfect_sound.png
http://imgs.xkcd.com/comics/map_of_the_internet.jpg
http://imgs.xkcd.com/comics/cat_proximity.png
http://imgs.xkcd.com/comics/color_codes.png
http://imgs.xkcd.com/comics/regular_expressions.png
http://imgs.xkcd.com/comics/command_line_fu.png
http://imgs.xkcd.com/comics/perspective.png
http://imgs.xkcd.com/comics/right_hand_rule.png
http://imgs.xkcd.com/comics/bill_nye.png
http://imgs.xkcd.com/comics/youtube.png
http://imgs.xkcd.com/comics/reno_rhymes.png
http://imgs.xkcd.com/comics/what_xkcd_means.png
http://imgs.xkcd.com/comics/regular_expressions.png
http://imgs.xkcd.com/comics/brain.png
http://imgs.xkcd.com/comics/cat_proximity.png
http://imgs.xkcd.com/comics/the_problem_with_wikipedia.png
http://imgs.xkcd.com/comics/romantic_drama_equation.png
http://imgs.xkcd.com/comics/e_to_the_pi_minus_pi.png
http://imgs.xkcd.com/comics/nintendo_surgeon.png
http://imgs.xkcd.com/comics/blanket_fort.png
http://imgs.xkcd.com/comics/random_number.png
http://imgs.xkcd.com/comics/small_talk.png
http://imgs.xkcd.com/comics/valentines_day.jpg
http://imgs.xkcd.com/comics/lisp.jpg
http://imgs.xkcd.com/comics/open_source.png
http://imgs.xkcd.com/comics/swingset.png
http://imgs.xkcd.com/comics/resonance.png
http://imgs.xkcd.com/comics/graffiti.png
http://imgs.xkcd.com/comics/hamiltonian.png
http://imgs.xkcd.com/comics/collecting_double_takes.png