Underused Themes

I don't think it's hard to find underused themes at all. Here's some I'm working on that are very uncommon:

A game where the players are CPUs in a parallel processing computer, which all happen to be insane and trying to make each other crash so they can have all the system resources (actually my most tightly themed game, it's pretty cool I think!).
Another is about construction but not in a generic sense, rather each player is a carpenter and you're competing to build specific room blueprints in one big house by laying tiles and playing blueprint cards (with cards like "subcontractor" and that sort of thing).
Another is a completely botched piece of crap about courtroom drama (i.e. play evidence cards and witnesses) which seemed to start off so good too... darn. Good theme though, because real courtroom action is really a sort of game with rules, but a strong human element.
Another is about publishing children's books.
Another one is I suppose just the usual fairy tale theme, but it's about a fairy tale divorce (who gets to keep the pumpkin stagecoach?).
Thanksgiving Dinner, a game where you have to arrange the family around the table so as to cause the least conflict.

To find other themes, you just reach out into the real world. There's SO much stuff people do (or non-people do) that could be easily mined for games. Skateboarding, pro wrestling, any other sport, managing any sport, teaching (dealing with bad kids and spitwads), being a motivational speaker (scoring for how rich the people you try to motivate get?), grocery shopping (first person to complete their list), bacterial conflict with white blood cells, how about erosion as an odd one (you use wind, water, and the occasional earthquake... maybe each player is trying to shape their continent to fit a certain pattern), gardening (been done a fair amount I suppose), bullfighting (it's a sport, but also a reminder to think of very odd sports! Like jai-alai or however you spell it), garbageman, newspaper delivery, confession (giving out the right number of hail marys or whatever according to the sins... yes, you could get in trouble making this game!), finding a parking spot and then remembering where you parked afterwards, being a landlord (deal with angry tenants, fix things with your limited money only when you must, evict deadbeats), running a phone company (like train games, you want to connect the most places), digging for oil (getting the rights, gambling on good spots), running for office, pork-barrel politics (try to get things snuck into bills to benefit your constituents or yourself, help out lobbyists so they'll give you even more money)...

Okay, I'll stop. None of those are broad like "space war" as a theme, but that's good. I think a good theme is focused, so that the mechanics almost naturally derive from it, and players really connect with what they're doing. My courtroom game for example came from playing Battle Line and noticing the rule about how you can win a line by proving, via cards that have been played, that your opponent couldn't possibly beat your meld. That's a perfect courtroom concept - play out evidence cards in different ways, and thusly like in a real courtroom, prove beyond a doubt that the killer couldn't have been there at that time. I still like the concept, but my mechanics just fell apart. I'll try again someday, I suppose. But I saw that mechanic and immediately I thought of a courtroom setting, the player is literally trying to prove something. Vice versa, you have a theme and it suggests concepts. Like the phone company theme above immediately made me think of those crayon-based train games, where you'd put up phone lines trying to connect the country (and maybe move your little "can you hear me now?" guy around for bonus points).

Actually, that parenthetical aside gives me another cool concept! Cell phone companies. Instead of putting lines in, you put in cell towers, which then cover a radius. Maybe the rule would be that your cell tower radius can't cover the physical cell tower of your opponent (physically implemented by making the towers push-pins with translucent plastic circles sticking out their radius), and each radius of yours must overlap somewhat with an existing radius of yours. Hey, I like it...

I've recently done first drafts of games with the following themes which I consider to be unique or intruiging:

1.) Elephant polo
2.) Birds on phone lines
3.) Network Hacking
4.) Genetics
5.) Cloning gone bad
6.) Real-time murder mystery deduction
7.) Making B-movies
8.) Self-Mutilation and Canniballism for fun and profit
9.) Fashion Design
10.) Rocket-powered ice skating

I think there's no end to unique themes. Just look around, or open a newspaper. Real life's pretty unbelievable, really.

Yeah, well, I recently designed a real-time card game with a theme of auto-cannibalism, where you're trying to eat as much of yourself as possible before shock sets in. You'd be surprised how a simple discription of the theme makes people want to sit down and at least try to go throgh the game once.