Unga's got it. . .if you want something fairly "modern" with mag wheels and liquid cooling. If you want something more vintage-looking with spokes, I'd vote for an XS650. If you luck into an SR500, grab it. Biggest advice is not to grab something just because it's available or the price is low. Hold out for something you like, because you're going to invest in a lot of specific tools, manuals, and knowledge for whatever bike you pick. Four-cylinder barn bikes may not be any more expensive to buy than twins (or singles), but they're wicked expensive once you get into them. . . lots o' pricey little parts will probably be needed, like carb rebuild kits, and if you need a matched set of pistons or rings, whew!