UFW (Uncomplicated Firewall) is the default firewall (iptables) configuration tool for Ubuntu and while it's a great tool, it might scare those not very familiar with the command line. Gufw on the other hand (a graphical user interface for UFW) makes UFW truly an uncomplicated firewall for Ubuntu and lets you easily allow or block pre-configured services, common P2P or individual IPs or ports and so on.
GUFW 10.10.1 has just been released for Ubuntu 10.10 Maverick Meerkat with a new feature called "Listening Report" which monitors your connections.
If you need help configuring GUFW (although everything should be pretty straight-forward), see the Ubuntu documentation on using GUFW - the screenshots are not up to date but most stuff should still be applicable.