Let's talk supermotos for the street.

Anyone who's ridden a dirt bike knows how much of a thrill they can be. One designed for road racing and made street legal is a recipe for hooliganism in the right hands. Lightweight with incredible acceleration (if lacking in the top-end of sport bikes) has led to the slogan of "fun at any speed". Supermotos are easily flickable, give you a huge vision advantage in traffic because you sit so high up, and can handle bumps, jumps and terrain that would break the suspension of a pure road bike. Also, they take crashes very well. Trust me, I know.

Also, wheelies.

superretards.com

So now you want one. There's tons to choose from, right? Not really, here in the states anyway. There's actually only one OEM still making a showroom sumo, and that's the DRZ400SM. The tech's about 10 years old and it's still carbed, slower than every other 250cc and up bike other than the KLX250X. The advantage the bike has is it's dependable as hell, has incredible service intervals, and a single carb is easy to work on. Plus the aftermarket offering for parts is cheap and vast.

DRZ400SM - photo from topspeed.com

Speaking of the KLX250X...You don't want one unless it's all you can afford, or it's your first bike. There's a reason they're unbelievably cheap used. They're the worst performing sumo out there. Like the DRZ, they are dependable however. Just slow.

The second most available purpose built sumo is the WR250X. It's much more modern than the DRZ, similarly priced, and makes similar power, all with a 6-speed transmission. They're very comparable though, the difference comes down to whether you want EFI or a carb, 6 speed or 5.

WR250x - yamahawr250x.com

After that you've got your 450 Japanese motocross bikes converted to street legal sumos. They'll sometimes pop up on craigslist, but you can make your own out of your own dirt bike if you're mechanically inclined. It'll cost a lot of time and a fair bit of money though, as compared to letting the other guy do the work and then snapping it up on craigslist for far less than they put into it. They have service requirements that will punish you if you don't keep up with them, so beware.

Finally, you've got your exotics. KTM makes amazing sumos, the 690 is highly coveted for it's speed and relative dependability, and there are 450 and 500cc supermoto racers converted to road use floating around out there. The Ferarri of the sumo world though, is the Aprilia SVX550. Wickedly fast, they are known for being extremely unreliable and expensive to fix. If you've got the money though it's the fastest you can buy. Husquevarna makes decent sumos and enduros you can convert as well.

KTM690LC4 - gdefon.com

Here in the states your best option for looking for sumos is craigslist, as about every sumo you can get is used, unless you want to buy a new motocross bike and spend another few grand converting it. Hopefully this guide has given you some ideas as to what's out there and what you'd like to get.