I'd like some suggestions of good community fish that like to be in the middle of the tank?

I'm a fan of the rasbora family of fish myself because they tend to be both tough and friendly, and half decent schoolers. Ones like harlequins, hengels, spotted, etc. can really work out nice. Other options you might consider are glass catfish (excellent, tight schooler), pencil fish, and of course, most fish from the Tetra family tend to be mid-dwellers, though I'm not much of a tetra fan myself.