A few that are standouts for me, some of which have already been mentioned:
RadarScope - an absolutely fantastic Doppler wx radar app that covers the entire country. It updates as quickly as the radar site you've selected makes new data available, which, at least for here in SoCal, means every minute whenever there's precipitation in the area.
TideGraph - a fairly simple and straightforward presentation of tide data which is a must have for fisherman, sailors, surfers or anyone who lives near the ocean.
SkySafari - a fantastic stargazing app that is packed with information. Dead simple to use and automatically adjusts to your current location. Lots of fun for camping trips. It's not inexpensive, but does occasionally go on sale for a super price (sometimes to coincide with notable anniversaries in our history of space exploration).
Honorable mention goes to Wobble. Not exactly what you'd call highbrow, but definitely good for a cheap laugh.
Some fun games: Implode!, Angry Birds, Fragger, The Deep (pinball), DeerHunter (and DH: Safari), and Let's golf!