As you know, anyone involved with the GP class has been working on 800cc’s for the 07 season, it’s all speculation at this point as to how much of that technology will filter into the open market. The YZR-M1 hasn’t been offered to the public yet (and doesn’t really look to be), but some of that technology is in the R1. At this point we can only hope and pray (to every god in existence) that the 800cc GP machines will bring a resurgance to the 750 class. I think the Suzuki Cup is the only series that is specifically for the 750, and only for their own machines - and I can’t even say that is still going.
I beleive that Yammy is pretty far along with their program, and I think that Ducati is leading the pack as I’m pretty sure they actually tested a prototype a couple of months back, which is not surprising as they have generally always made “odd” sized bikes (not your typical 600 and 1000’s) - they were producing 800cc bikes as recently as 03. The last 750 made by Yamaha was 01 (the R7 which was basically a stripped down race bike to begin with) so in production terms, their last 750 was '98, which was my beloved YZF, produced from 93-94 and 96-98, the last design change coming in 95 for the 96 season. The YZF750 actually started as a race bike way back in 88-89 and it took until 93 for Yamaha to put it into production - hopefully, it won’t take that long for things to trickle down to the rest of us this time around.
As for which one, it would be the oldest one, and for that 750 WORKS bike I linked on BPN, I’d consider selling two.