This app just keeps getting better.  Beejive IM has been my favorite Multi IM chat app since back in my blackberry days.  I like the ability of using wallpapers for backgrounds and the ability to change the chat bubbles.  The push notifications are a great feature as well.  I highly recommend this one.

“BeejiveIM is the most reliable and user-friendly mobile IM application on the market for your iPhone or iPod Touch, featuring desktop-like instant messaging and always-on efficient networking.

Works with AIM®/iChat®/MobileMe®, MSN®/Windows Live®, Yahoo!®, Facebook, MySpace, GoogleTalk®, ICQ®, & Jabber.”

App Store link

via Beejive IM *updated* Allows send video support for iPhone 3GS | iPhone News & Reviews.