You probably have people who are hard to buy for and could use a bit of inspiration for ideas. Try 2,100 Gift Ideas ($1.99). It offers gift ideas from hundreds of online stores. The gifts range from electronics and jewelry to things you might not even have known existed. You can choose gifts from various categories, such as Mom, Dad, Kids, Him, Her. Plus, you can sort by price so that you only see suggestions in a particular price range. You give your iPhone a shake, and it then starts serving up gift ideas.
[Edited this 12/9/09 to reflect the app's new name.]