Here is a great article from Bennetts - BikeSocial with recommendations as to what to look for if you are in the market for a modern classic motorcycle. I'm glad to see that prices are much more reasonable than they were a couple of years ago - when a bag of bolts would cost a king's ransom!
This is their shortlist - & I'd pretty much agree:
1996 Suzuki GSF1200 Bandit
2005 Suzuki GSX-R1000K5
1985 Yamaha V-Max
1993 Ducati M900 Monster
1994 BMW R 1100 GS
For my money - I'd add this to the list: 1983 Honda VF750 SC (Sabre). This was one of my fave big bikes in the day. Now a minter (like these: Bike1 or Bike2) is £2.5 to 3.5k. Doer-uppers start @ £600! They did have their issues (OK, major issues - camshafts!), but when sorted (& they invariably are - or they wouldn't be around 30+ years later) they are cracking bikes. Santa - please take note... ;0)