d20 Conan sounds right up your alley (particularly if Grim Tales is also on your radar). The second printing of the rulebook (entitled Conan: Atlantean Edition) with all the errata incorporated is just about to be released so now is a good time to buy. One nice thing about Howard's Hyborian Age is that, in true wierd tales fashion, he had diverse cultures sharing the same globe: this nation over here is late-midevil France (knights and all) while that nation over there is stone age savages and everything in between. Because the rulebook was designed to accomidate adventuring anywhere within the mythos the rules can easily be adapted to most of your low-magic adventuring needs. I'm a big fan.
Failing that, I would go with d20 modern over DnD. It is easier to add fantasy elements back into modern than it is to gut them from DnD.