i have been a long time user of meebo and pidgin portable to get my IM fix but today i stumbled across Meebone which is part of google code.
i love meebo and my main frustration with it is the need to have a browser open but Meebone is an adobe air app that runs meebo and ive been using it today and it appears to be really good. it needs a few things like it does not appear to have any sounds to alert you of messages but im sure that will come.
EDIT: well i used it for awhile then i got annoyed at it, no sounds + no dual screen support (which i admit is a fault to do with adobe air rather then meebone. Then i found Digsby
Google Code: MeeBone