Flats may give you the tone you are looking for, and the brands that Scott mentions are all good ones.
Another opption for a rounder, less jangly tone might be pure nickle roundwound strings. (not nickle wound steel, but "pure Nickel") Fender is the most common brand for these under the "Original Bass" label in 3 different tensions. Rotosound also makes a good set, and I assume other brands do also.
They start out reasonably bright, but very quickly (within a week in my experience) they warm right up. I like a round, not jangly tone, and they are now my exclusive strings on nearly all my 4 string basses. They sound great for recording and playing live. As an added bonus, Nickel is a very soft metal, so it will prolong the life of your frets.