Dodgeball.com: this Google-owned site turns your cell phone into something like location-enabled AIM. You set which of 27 cities it supports, and you can let your friends know where you are using SMS email. You can also try to find a bar or restaurant by sending the name, and it will return the address. I’ve signed up.
Farecompare.com: you provide two cities, and it tells you not only which airline has the cheapest flight, but on which days and flights you can actually use the fare, and the fare basis code, which is what you need to have a travel agent actually issue the fare. Great!
Portableapps.com: Site where you can find portable versions of open source apps that you can save on your memory stick and run anywhere, taking your preferences and data with you.