Most major banks have an app. They're secure, and are just as functional as their sites.
I had a task killer, but uninstalled it and my phone was much faster. This was on a droid though.
Anti-Virus...I don't believe it is necessary.
A good file manager (explore phone contents like windows) is a good idea. Astro is a popular one, the aforementioned friend with the Thunderbolt uses something like ES manager, I don't know.
NASIOC has an app too.
Shazam is good for identifying songs while they're playing.
That's all I really use.