Keywords are critical in getting your app discovered in the app store so here are two great websites I’ve found to help you to optomise your keywords:
http://www.Appcod.es : This site allows you to enter in keywords and see how popular they are in searches people are doing, how many apps out there you will be competing against for these keywords and also how likely your app will display for these words if you use them. It’s also got a great feature on reverse engineering successful apps.
http://appstorerankings.net/ In this site you type in the name of any app and this site does its best guess to tell you what keywords that app is using. I checked out some of my apps and it’s actually pretty accurate!