Forum Moderators: rogerd
I preferred the 2.x versions to the newer version 3 but that's probably just reistance to change ;).
Gossamer Forum (from Gossamer Threads) might be of interest too if you are looking for something different.
Choosing forum software is a personal process - I'd recommend visiting forum software sites and then checking their feature lists (to be sure they'll do what you need) and example sites (to see what some other sites have done with the product). If you expect a high volume forum, be sure that you can see good examples of busy forums in your preferred software. Some software tends to hit the wall at higher volumes of posts/traffic/members online. If possible, download a demo to play with.
Note, too, that your server may determine your direction. If you are on a Linux server, the ASP forums probably won't be viable choices, for example. Good luck!
YaBB 2 is still Vaporware, but it shows a lot of promise, especially when it comes to reducing server load.
And people are familiar with it. It's one of the most heavily used BBS packages out there. And if you're worried about the chunky "look-and-feel" it has out of the box, then you should check out the template vault and the massive number of mods available.
Also, from an administrator standpoint, Perl is 10x easier to hack and mod than PHP, any day of the week.
Here's the tricky part - to have the archive function properly, PHP must be compiled as a module on your server. This doesn't seem to be SOP at most hosts, so expect some additional effort on their part. On a shared server, they may not do it for you. You'll also need GD installed if you want to do image-verification during registration (to prevent bots from signing up). Alert the host about this before they compile PHP; otherwise, they'll have to do it again.
I don't think there are any must-have hacks since vBB is quite full-featured, though you can browse vbulletin.org to see what's available.