Yamaha FJ1200
'Twere about 1989 when Yamaha updated the long-legged torque monster FJ with a 17-inch front wheel, etc. What started out as a semi-cutting-edge open-class sportster ended in '93 a beautiful sport-tourer (with ABS, even). Read the ad. You want the one with "low miles" and "backrest," not the one with "stage-three jet kit, runs nines."
Kawasaki GPZ750 Turbo
Prices for these things are all over the board. Some people think they have a collectible and want big money; most think they have an old red bike they need to get rid of. Either way, the relative complexity of the injected turbo kept most wrench monkeys at bay, and a few low-mile examples of this historically important bike are out there for a song.
Honda CBR1000F
The second-generation CBR1000F returned to the United States in 1990, having lost its "Hurricane" appellation. It's not quite as powerful and modern as the current CBR1100XX, but it's close. Like the XX, the CBR-F was always more sport-tourer than pure sportbike, and as a result they tended to be bought by more, shall we say, mature riders. You can scare up nice ones for $3500 or so.
Higher End
$4000-$6000
Yamaha YZF600R
The '97 iteration of Yamaha's middleweight sportbike carved out a niche for itself that's now vacant (except for the new ones Yamaha still sells for $6999). Not as light as the current crop of 600s, the YZF exchanges the final 10 percent of performance for about 50 percent greater everyday ridability. Perfect low-milers can be had for well under $5000.
Harley-Davidson Sportster
Need a fast Hog? Drive a bargain on a base Sportster, then bore those cylinders out, throw in Wiseco pistons, and you've got yourself a 1200 that rips-OK, goes a little faster. Or Buell will sell you heads, pistons and cams that bring your Sportster up to X1 spec. Five Gs will get you a clean, five-year-old 883.
Yamaha YZF1000R
Yes, the R1's a superior track machine, but if we wanted to do a little traveling on our 130-horse street ripper we'd opt for the previous generation. The YZF-R weighs 50 pounds more, and that extra weight consists of a better place to sit, a bigger fairing to hide behind, etc. Steal one for less than $6000.
Suzuki GSX-R1100
Notice a trend here? Liter-class Japanese sportbikes have always been expensive and nicely put together, and as a result have tended to be bought by affluent riders who didn't abuse them too much, frequently due to the no-time-to-ride syndrome. Take advantage. Apparently we won't be seeing the likes of the '95-'97 dreadnought-class GSX-R again; a great fast, smooth sportbike for less than $6000.