Haven't found too many decent VST synths and instruments, but what ya'll might want to think of is SOUNDFONTS. You can use them in FL too and you're going to get a lot better stuff out of that (from what I've experienced personally). Do a google on soundfonts and you can definitely find a shitload of them for you.
Try sf2midi.com, that's where I got a LOT of free ones, a lot of them are pretty good if you don't mind tweaking just a little bit.