I'm having a blast finding some great iPhone apps! I'm not sure how many are the same between the US and UK, but let's share ideas! Please post the name and a brief description of the app.
My favorites:
Tip Calculator: self explanatory
Pennies: Input a budget amount and the gas gauge meter tells you when you're getting close to "empty."
Have2P: Finds restroom locations
Barnes and Noble: Take a picture of a book and it'll tell you if they sell it and how much it costs
PixSter: Upload pictures to Facebook
Camerazoom: self explanatory
Shazam: Listens to a song (doesn't find my friend who has released CDs, but she's not been on the radio yet) and tells you the artist and song title. I love it for reminding me of songs to download later.
Dunkin' Run: sends invites to friends and they can place an order with the online menu and I can print it out or read it off my phone. Everyone I've used this with loves it!
iEmoji: cute little emoticons
ScrabbleSudoku LiteScramble: The Facebook game where you have a grid of letters and have to make words.
Tap Tap Revenge: like Dance Dance Revolution, except you just tap the screen.
Guitar Tuner: plays the notes for you to tune your guitar