You can recommend either one from the Free Catagory or one from the Pay Catagory or one for each catagory! Basically just tell me what you think is best.

From the Free Catagory, there's phpBB, SMF (Simple Machines Forum). As for Pay Catagory, there's IPB (Invision Power Board) (This board is base on this!), vBulletin and so on. These are just some of the popular ones. But what do you think is best?

I'd prefer we discuss about software that uses PHP and MySQL. After all they are the most common and popular. However, if you do find a good one running on ASP, go ahead and tell us!

Just interested to know. Thanks everyone!

For paid forums I would recommend Invision Power Board.

For open source forums I would recommend either SMF or PHPbb depending on your needs.

Skins? I make my own.

phpBB3, or SMF will both do fine for a free forum. phpBB3 tends to be more user friendly in my opinion, but according to everyone SMF is the most stable and secure. I recommend Invision Power Board for a pay forum, the licenses are quite expensive though in some cases. I think a free forum will work out just fine for you when you are starting. There are TONS of themes for phpBB3 but not as many for SMF. And you can make your own skins too. phpBB3 skins tend to be easier to code, SMF is somewhat harder which is why there aren't as many themes. Hope this helps!

The features in vB 3.7.X are a nice improvement and quite an update over 3.6.X and lower versions. May be forth a look if you haven't seen 3.7 yet.

Are you going to be using a portal or just straight forum?

Thank you Moc and Pcwiz! I though so that it would be about the few I've mentioned above. I've tried the latest stable versions for both phpBB and SMF. And just like Pcwiz, I find phpBB better in terms of usage. But the one thing I really dislike was that the default theme came with post profiles formatted to the right side of the post. That was easily worked around though. Oh and thanks for the links, Pcwiz!

Deleted! You scared me! At a quick glance over the last post "by: Deleted", I thought my post was deleted!
Anyway, no it's not going to be a portal just straight. I'll have a look at vB 3.7. Thanks.

Well I would say PHPBB if going for a free software. It is definitely a secure piece of software and easy to Theme
If going for paid its definitely IPB (Mostly because that's my base for all my Forum Addons and Custom Work )

Thanks! For paid, I also prefer IPB. But vB is close enough too.

phpBB. Open source can't be wrong, right?

when I first started I was using phpBB2, and now I upgraded to phpBB3 and I must say phpBB3 is very good.
What I love about phpBB, is how you can just customize the hell out of it, vBulletin, IPB... you can also do the same, but with phpBB (at least to me) the sky is the limit... plus its free.

Just try it out on this host and make your opinion : create a forum

IMHO PHPBB is the best free one. It also has quite a big bunch of hacks and mods. If you want a full CMS based on phpBB I recommend Icy Phoenix.