If you are annoyed by the new Facebook sidebar-chat, you can get your old chat in a new window. Once logged in, go to this URL https://www.facebook.com/presence/popout.php aaaannnnd Go Online! Chat!
There is another way to get your old chat back, but this involves a small add-on for your browser:
– Greasemonkey – for Firefox (the one I’m using). After installing the add-on, you need to go here: http://userscripts.org/scripts/show/107159 and install the facebook chat reversion script.
– Facebook Sidebar Chat Reversion – for Chrome.