Well even though I linked to those flats, I personally don't like flats. I just I like to have some life, some zing, some punch to my sound so I use nickel rounds. Someone else suggested flats, and those are a great deal, so there they are
If you like rounds, you are NOT going to find a better deal than either of those others ones I linked...the LaBella 3 pack or the $10 Progressives. Progressives have a nice warm grit to them, nice and punchy.
If you want flats, those LaBellas are fine or BSO has some light guage GHS flats for $15.
If you want a cross between flats and rounds, try GHS Pressurewounds. No zing like rounds, but no dead thunk like flats.
GHS Boomers are brigther than Pressurewounds, but duller and thicker than most other rounds.
DR Sunbeams are a nice mellow nickel string with round core for lower tension and a nice supple feel.
www.bassstringsonline.com has the best selection I've seen.