I'll also second the BMW thoughts, although I might expand my year range into the 80's. I'm a big fan of the R100RS...R90S wouldn't piss me off either (more $ though). BMW developed these bikes a lot like Porsche developed the 911. Over the years the basic design stayed the same, and they made continual refinements.
A nicely set up boxer twin is a pretty sweet ride. Reasonably sporting, and very comfortable, plus they are built like tanks. I also think they are stupid easy to work on should you decide to DIY. Its fun to cross reference parts using the Bosch #s. I had a faulty starter solenoid...BMW wanted over $100. Found it was the same bosch# as an old aircooled VW...$30 at the local foreign auto parts store.
I've tried two classic Guzzis (1979 and 1983) and they were ok, but I'd rank BMW higher. If you want something rare, old and Italian, check out a Laverda 750SF from the early seventies.
