It's a good question. I've got a good sized basement, but wasn't using it that much until I upgraded a 20 year old couch with some nice leather home theater seat recliners, and added 2 32" TVs along with the big screen so I could have more games on. Totally worth it to me because now I spend every fall Saturday down there, and use it more other times. I think you want to make it appealing enough that you want to use it. I had just as nice of a TV upstairs so without something extra I didn't bother going down there much. I put up some Husker memorabilia and bar signs and stuff and think it looks pretty cool now. Mini fridge, you bet.
Most things are just whether you think you'll use them, or really like the look, and have the space and money. Pool tables especially take a lot of space though they look great in a game room. When I built my house I made sure I had room for one but if/when I ever move I won't do it again. Darts, you just need an alley way and a bit of wall space, and it's lower cost, and I use that just as much.
I just this morning ordered a Stiga hockey game. I'd love a dome hockey table but they cost a lot more and take more room, and I've got a perfect counter with space on each side for the table top game. I had a classic game in the 60s when they were built great, but it must not have made a move somewhere, and a cheaper built game in the 90s that basically fell apart when we tried to play it this weekend. The drawback is that unlike pool, darts, pinball, etc, which you can play by yourself as well as others, you need an opponent for hockey. But it's so damn fun, and looks good too. A lot of guys come over and look at the pool table and nod approval, but when they see a hockey table they really light up.
Seems like a pinball table and jukebox could brighten up a basement nicely but I never really got into pinball and would just rather pipe music through my home theater speakers with an mp3 player so I just added some rope lights to kind of get some lighting effect.
I always liked trains and have a nice set up at the other end of the room where my pool table is. It's a space hog but a big attraction when I have people over, plus I'm really proud of showing off all my son and I did on it, especially the mountain with tunnels we made.
Whatever you do, just make it yours. Use the space and funds for things that you like and you'll enjoy it more.
I love the 3 TV ideas.