Doppler Radar
SysStat
GeoLocate (looks up IP addresses)
That's about it
P
Accu Weather - for 3 different cities
SunLit Earth - to remind me what time it is in Europe when I call friends and family from the US
Gas Price Watch
iStatPro
I have turned off all my other widgets since they do use up a surprising amount of memory and I only have a G4 iBook... at least according to iStatPro, that is.
grim

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic