Cut through the crap, when it comes to Mac OS X apps! I've spent time talking to friends, and testing out applications. These are my favorites. I don't post everything; on the contrary, I put up only the best of breed. You won't find any junk here, other than maybe my design.
Suggest a KILLER app.

IM / Chat

#{app.name}
Adium
Hands down, the best IM client for OSX. I've tried others, and Adium just performs. It understands a ton of IM networks, and offers OTR encryption between peers. If you're comfortable giving up the fantastico superrific video features in iChat, then this
 
#{app.name}
Colloquy
Get on IRC effortlessly. Lots of support for extras, scripts, and themes as well. The biggest plus for this application is that it has support for SILC and other secure chat mechanisms. This has clearly been polished.