Dude, what fun. +1 more on the mancave title, BUT use the term for internet searches and ideas.
Here are some personal suggestions:
Keep the area open, don't create walled off rooms.
Install a bathroom, if that's an option. Completely different vibe (buzzkill) if a guest has to go upstairs to use the bathroom.
Movie / Gaming area. Doesn't need to be a full out 'theater'. The 100" screen, speakers/sub and seating is perfect.
Game ideas: darts, shuffleboard, foosball, arcade, pinball, driving cabinet, pachinko, slot machine (or software on a touchscreen), poker table
Other Possibilities: pool, bumper pool, (indoor) cornhole, skeeball, ping pong
If you drink, build a bar. If your friends drink, build a bar! If your gf drinks... build a bar!!! I can sit about 11 at my bar and the whole family enjoys it. If families come over, usually the parents hang at the bar and the kids play the arcade, pinball, foosball, xbox, etc.. We've got a large screen behind the bar and its comfortable enough to sit alone, with my wife or with the family (some dinners are eaten at the bar).
Beer. I've got a glass door merchandiser and a 2 tap kegerator. No need to choose one or the other.
Multiple TVs - Great to be able to view from playing areas. It's easier to select an opponent when they know they can still catch the (sports) game on the TV while playing darts, etc. I have one above the shuffleboard table, which allows players to conveniently view the baseball/football game .
If you're thinking of DJ lights, then you have to be thinking of music. One thing that I did, and am real glad I did, was to install ceiling speakers and a speaker selector. I've got about 5 pairs in the ceiling. The speaker selector allows me to control which speakers are on and which are off and to control the volume on each pair. I've got speakers in the bathroom too so the party doesn't stop!
Oh...and a fog machine goes great with the laser based DJ lights. : )