Many will consider this way excessive, but I use

-b 320 -k -q 0 -m S .

Basically the top quality possible. Quite large mp3 files. Problem is, for me, I can hear the difference, or maybe I THINK I can hear the difference. Still, form my personal pnt of view, that does not make any difference right?

Forgot to mention that I use Lame as you could guess, with Audiograbber. I found it very very good, and ended up registering it. Hope this helps.