Berryvine has a 7-day trial, and you can purchase the license on Handango for $12.50US.
Here's the link for more purchasing info.
BerryVine Messenger by RSIC - Handango Blackberry Software
One quick note on this:
You
MUST have BES, or MDS/TCP capability to use this.
You can install OTA at bb.berryvine.com
or via DM via USB/Serial at berryvine.com/download.asp
Good luck if you go with it. Like I said, for the short time I've been using it, I like it. It allows you to Minimize without signing out too. ;)