As for acoustics, Roland has good acoustic sounds. The Edirol softsynths are based on Rolands, I dont know if they are exactly the same but I assume they should be. My measly Roland JV 1010 has some great Acoustic sounds, good enough to fool almost everybody.
THe TTS-1 that comes with Sonar 4 is pretty good. It's more a matter of being able to play or program the parts correctly. Most people let the individual notes ring out too much when they are playing them.