Right now the primary mods are vBShout and vBShop for me (although I use several others as well).
vBShout, my members like... a lot... hehe So they hang out on the website and just in general BS there. Some people think it takes away from posts, but really.. I don't see that. It keeps people around and if something is post worthy, they post it.
vBShop I use extensively for my site, it handles all of my usergroup changes. This way I was able to give specific people access to "gift" usergroups to other people, but not give them access to the adminCP. This has relieved a LOT of the work from myself and put it onto the various areas that people are working in for me.
One of the other things I plan to do is let my users have their custom shops for the different games we play. This will allow them to handle their ingame inventory outside of the games (some games are just bad at it).
Another useful mod is the Advanced Thanks/Like mod, it's starting to catch on and my users are using it more and more.
Of course, I also use vBActivity, vBCredits, vBOptimize and InfoPanels as well (and others actually). But these are (for me) the most important mods. I need to redo a lot of my site (already started with a new theme) and work on some of the integrations and different ways to use the mods myself. There's so much potential in these mods for new uses that weren't even planned (like the way I use vBShop) that it'll take me a bit to do, but at the same time... will rock when complete. =) My site is at
www.darkhandofvalor.com if you're interested in seeing some of the mods in action (You'll need to register if you want to see most of them though, up to you).