Hey,

I´m very picky about sound accuracy/quality. I´ve probably bought just about every Softsynth/ROMpler/Hardware setup you can get. Real Tracks makes it even more important that you use high quality sounds. So we all pretty much know there are many ways to accomplish this.
Mac recommends the Ketron SD-2 Hardware synth which has gotten many rave reviews and the price seems right too. I have been using Kontakt 3 from Native Instruments, which is a soft sampler that lets you use many different sample collections. I´ve also been using Synthogy Ivory for Grand Piano, Spectrasonics Trilogy for Bass, and FxPansion BFD Drums and Percussion. I also use Chris Hein Guitars, which goes a long way in helping your midi guitar tracks sound real. If you use Cakewalk Sonar, they have a really great GM Softsynth called the TTS-1, which is a high quality copy of the Roland Sound Canvas. I like it because it responds to midi patch changes. Although some like the Coyote Forte Softsynth, I´m not fond of it. I know lots of people like using the Garritan Jazz and Big Band PLug in, but I think you can do better ( I own and used the Garritan J&BB for about a year, but I´v e since outgrown it)
My advice: Find a vedor who will take your return, then try some different Plugins and the Ketron, as well as Yamaha, Korg & Roland stuff. Be careful about ¨Restocking Fees¨, its easy to get ripped off if you don´t read the fine print. Also, don´t look past Physically Modeled plugins, they are starting to sound better than Samples!

Hope this helps you!
Ed