Yelp is a great app for getting local knowledge on where to eat, drink, and shop. You can find places nearby, read or add reviews and photos, book a table, and get directions.
Filters include price, distance, opening hours, rating, and whether it provides deals or offers for check ins.
There are some great features. With Monocle (only available on some handsets), you hold the phone in a certain direction and it displays restaurants in that area. There is also a RSS feed of recent activity nearby.