Castrol RX Super 15w40
Chevron Delo 400 15w40
Mobil Delvac 1300 Super 15w40
Pennzoil Long-Life 15w40
Quaker State 4X4 Synthetic Blend 15w40
Shell Rotella-T 15w40 (my personal favorite)
SuperTech 2000 (WalMart) 15w40
Valvoline All Fleet 15w40
Castrol Syntec Blend Truck and 4X4 15w40
Full Synthetics - for Maximum Protection
For years Mobil One 15w50 has been a favorite of motorcyclists. In recent years it has gone from its original formulation to an improved SJ "TriSynthetic", and more recently as SL "SuperSyn." several of us have received conflicting information on this new "flavor" of Mobil One, but the consensus appears to be that the new SuperSyn has additional friction modifiers and may no longer be a good choice for motorcycles. However, I have heard from several VFR owners still using it with favorable results. Therefore, YMMV. Mobil naturally recommends their motorcycle Mobil One.
A fairly new player in the synthetic market is Shell with Rotella-T Full Synthetic 5w40. It is not energy-conserving and according to Shell performs competitively with Mobil Delvac One full synthtetic, which means it offers even more protection than does Mobil One 15w50. A number of motorcyclists have reported to me good results so far with his use of the new Synthetic Rotella-T. I put it in my own VFR at my last oil change.
Important Note: Be sure and use the recommended viscosity range, e.g. 10w40, 20w50, etc. for the climate in your area. In general, to protect your motor use the heaviest oil you can that still meets the manufacturer's guidelines. For example, 20w50 is better in warm weather than 10w40, because it gives you a thicker oil cushion between bearing surfaces at operating temperature. For racing, a thinner oil will offer less resistance and thus more power, but will offer less protection.
I personally believe in these oils and use nothing else in my motorcycles. As always, you have to make your own, informed decisions.