i don't know about the 500... haven't had one for years, but the Mamiya 645 AF has built in light meter.. it handles like a 35 but gives you 645 size negs... I would guess other medium formats have that are AF probably have built in metering...
Some do and some don't. Blads probably have an atachment that you can buy (if you mortgage your house....)
If you are moving up to medium format you'd do better to buy a good handheld meter - the ones built into cameras are not all that hot.
it has spot and ambient capabilities...its a minolta. i havent used it much yet, but i got a bronica SQ-A and the viewfinder that came with it had no meter.
i would look at the minoltas, or if you want to shell out some serious cash, go for sekonic.
Most medium format SLRs have a variety of viewfinders to choose from; some have built in meters, and some don't. The difference in cost between a metered prism finder and an un-metered prism finder is usually as much or more than a nice hand held meter, so I agree with the above posts that recommend getting a hand held meter.
When I went looking for a Hasselblad 500 series camera I was looking for one with a waist level finder, but I found a deal on a very clean Hassy 500c/m with a metered prism finder for about what I expected to pay for one with just the WL finder. I've never been really impressed with the in-camera meters on most of the medium format SLRs I've used, but this one seems very accurate when compared to my hand held meter. I still use the hand held meter though; it's just a lot more versatile.
You can get hand held light meters for between $50 and $100; they usually have one style of metering. Meters with more features can get expensive pretty quick. If you are going to spend a couple of hundred bucks take the time to make sure you're getting what you need now, and in the future.
I use a Sekonic 508. It has incident, spot, and flash meter built into one unit, with a few other features: memory, averaging, custom settings, etc... It was expensive at the time, but cheaper than buying 2 or 3 seperate meters to get those features. It serves me well from my landscape photography to portraits with flash.