Depends what are you looking for exactly? Sylenth1, Massive, Gladiator and FM 8, are popular. If you want a nice cheap synth check out the Korg Legacy collection. They are only 32 bit and I doubt they will go 64 bit but they are $50 each or $200 for the bundle that's not a bad price considering all of the other synths I mentioned are about $200 each.