Walthers, Atlas, and Diamond Scale lead the HO turntable market in variety of materials as well as configuration. (Diamond Scale produces many pit and turntable assemblies in basswood.) From branch-style arrangements to full-radius track access, turntables let you make maximum use of anywhere from two to 20 tracks.
Examine turntable control systems as part of your research. Precise controls are, after all, your best insurance against collision. Several options, from simple to complex, help you manage traffic; some systems will warn you when you're literally on the wrong track. Roundhouse optional - it's fun to get running the turntable under your belt before you enclose it.