Back when the Windows Mobile version of the Palm Treo was still my favorite smartphone, I used an excellent Chinese dictionary to quickly look up characters. I haven't spent any time in China for a few years, so I'd kind of forgotten about Pleco. Thankfully the company didn't forget how important it is to have a highly functional Chinese dictionary. They've since added an iPhone version that looks and performs every bit as well as my old favorite from the Treo.
The app is designed to make looking up Chinese characters faster than you could ever do with traditional paper or type in dictionaries by using the handwriting recognition built into portable devices. As I've already learned, one of the biggest frustrations in learning Chinese is remembering the meaning of the thousands of characters. Looking up characters manually takes minutes per character with traditional characters. Looking them up using a stylus takes mere seconds.
Anyone who travels to Asia with an iPhone should definitely own this app for looking up characters. If you need to do the reverse, and write in characters to decipher them, there are paid upgrades to help you out.