I currently have both a Rolleicord and a Mamiya TLR along with several folders. I'd recommend a more Rolleicord IV or V or the similar Rollei or one of the other fixed lens TLRs mentioned. My Mamiya is a very good camera and can be used with a tiny tripod (compared to an SLR), but it is not a light little beast. The nice thing about the fixed lens TLRs is that they are great carry-around cameras (and much better used hand-held) even if you later decide you want an SLR system later. I also find it a whole lot more fun to use!
If you decide on a Mamiya, though, I'd go with a C220 or 330. They are cheap enough that there is really no reason not to go with a more recent camera.