My top Apps for iPhone are :
(1) World Now - A great application for weather around the world - Free App
(2) YouNote - Single App which allows text note, voice note, picture note, web note and more - Superb App - Free App
(3) iXpenseIT - App for storing all info about expenses, including photo receipts - Must have - Paid App
(4) ProLoan - Great App for calculating Loan EMIs and comparing the various loan scenarios. May be very useful in todays tight financial environment. It is a brilliant app - Must Have - Paid App
(5) Speedtest - Wanna check the throughput of your Edge / WiFi connection, try this. - Free App
(6) AppSniper - Discover new iPhone Apps everyday. It is much better than App Store to search new apps - Must have - Paid App
(7) Quickpedia - Browse Optimised Wikipedia on ur iphone. Whats special is to discover Wikipedia articles about places near your current location. Works even on 2G phone - Great App - Free App
(8) Discover - Connect your iphone to your Computer wirelessly and start using iphone as your storage device - Must Have - Free App
(9) HelloCards - Terrific App to send greetings from your iphone - Must have - Paid App
(10) Pinpoint - Find your current location on the map and mail it to anyone - Must have - Free App
There are many more great Apps for iphone available. However, I would mention about one app that Steve Jobs should anyway include in the next version of iphone release. It is QUICKGOLD - What a search app for iphone contacts, email, browsed pages etc - Superb one click access. Should have been part of iphone as default. To top it all it is a FREE APP. (But available only for hacked iphones).