I'm not familiar with Android / iPhone exclusivity but some of my favorites are:
Lookout Mobile Security - (Creates emergency backup of contents, locates lost device and anti-virus all in one)
News Republic - a MUST for iPhone or Android. Awesome news app that lets you search for you desired topics and save them to your home page. Also can pick the sources so you can weed out the biased stuff.
YouVersion Bible - If it's your bag it's awesome.
Opera Mobile - i like it better than the stock browser.
DropBox - If you don't know what this is already, it's super convenient to have it on your phone. Network storage that syncs data between computers and devices. 2GB free saves you in a pinch.
Google Voice - Free local #, Free Visual VM, Free Texting, what's not to like?
TuneIn Radio - Saved me last year when I needed to hear my team play on the other side of the country. Just pulled in the local radio from 1900 miles away. Awesome!
Vlingo - Voice to text for everything, emailing, texting, search. Great for driving!
USAA Deposit Mobile - if you bank with USAA you can make deposits by taking pictures of the checks. Amazingly convenient.
The beauty of Android isn't in the Apps. though. They're nice, but the real beauty in Android is the Widgets and customizability.
Welcome to Android!