As Facebook Chat now supports Jabber/XMPP, you can integrate it into your favorite chat client. I have been a big fan of Pidgin for more than three years now. Therefore I have mentioned the simple set of steps for setting up FB Chat on Pidgin.
1. Launch Pidgin, go to Accounts –> Manage Accounts and click Add… .
2. Fill in the Basic tab as shown in the following screenshot.
3. You need to make sure you have unchecked all SSL options on the Advanced tab.
4. Click Add and you are done.