If you want audio or videoconferencing, no.
Otherwise, there are many options:
Official MSN Messenger - does things like nudges, winks, custom emos, but no webcam support.
aMSN - does essentially everything except audio and videoconferencing (it does do no-sound webcam)
Mercury - similar featureset to aMSN
AdiumX - no audio, webcam, videoconferencing, but 1.0 does do custom emoticons. It's a multi-client app like Trillian on Windows, so you can be connected to AIM, MSN, Yahoo, and Google, for instance, all at the same time.
Proteus, Fire -- two more with similar feature sets to Adium
iChat -- can also get very basic text MSN through a Jabber gateway.
Of all those options, the most popular one here is Adium. If you're text only, it's a wonderful solution, and it's the one I use regularly. I did have aMSN and Mercury as backups when I had an iSight, and I do have MSN Messenger though, because it comes as part of Office.