Free forums.

[Inu^^]

Unlike invisionfree when you have those annoying ads at the top and can't be gotten rid of without paying, there is now another soloution around this problem.
iPBfree forums.
They're all the linked but these forums are a lot more professional than invisionfree and others like proboards. You get more addons like mini-arcades submerged into the forum by default. Also point systems and many, many more.
Since normally everybodies dream is to save enough money for a Vbulletin board, this is something nice to start of with.

ipbfree.com/home/

Enjoy!
~Inu^^

[Pumazooma]

You don't often get something for nothing. I wonder how they pay their server bill when it comes in. Most free forum hosts have some kind of compromise. One of the biggest being that if you ever want to move elsewhere you may not get a copy of the database.

Paid hosting really isn't very expensive. Look at this site. You can get enough bandwidth to start you off for only £20 a year! That's a much better bet than a free host.