Today's WSJ/Desktop Traveler Feature is very timely, with a bonanza of information relating to crossing items off the list above and generally seizing the day, with gusto, if you're into that sort of thing.
Dogsledding -- tour operator and school in Yellowknife, Canada (hi gwinky! hi str8!):
dogpaddleadventures.com
Swimming with sharks -- 5 day tours on an 85 foot boat to dive with great whites off Baja, Ca., with a shark sighting guarantee, and if you're uncertified, you can do the cage thing:
sharkdiver.com
Race car driving -- not Formula 1, but v-8 fiberglass Cobras (hi Thrasher!); schools in LA, Vegas (combine with #19 for a 2 in one), Houston, Phoenix, Washington, and Calgary:
racingadventures.com
For skydiving, dog sledding, airplane and helicopter charters, hot air ballooning, paragliding, ice climbing, horseback riding, safaris, dolphin and whale watching, white water rafting, fishing, scuba diving (and surfing, all manner of kayaking (hi bilmore!), go to
adrenalinepages.com. This site is very cool. The sections are organized into air, snow, earth, and water, with further categorization for photos, schools, gear, and stories.
And for motorcycle racing, buttboarding (hi again Thrasher!), streetluging, running with the bulls, mountain biking, surfing, snowboarding, and almost anything else that may result in scars, bruises (hi shape shifter!) and broken bones, go to
doctordanger.com 
