although not free, doom3 engine i find good to use. its easy to get custom assets into it, and it supports proper unified per pixel lighting, so your normal mapped models look class. good for modding, and bound to be made open source in the next year or so, as is the habit of Id.
i have also used source and unreal engine 2. they are ok, but both work on the principle of lightmapped world and vertex lit non-static meshes. i dont like that.
another option is
dx studio although i have yet to get stuck into it, we will be using it a lot in college this year. its cheap. about fifty quid for a pro licence if you are a student. and their free version works, but watermarks the release until you save it though a pro version.
ogre is just a rendering engine, and needs serious code skills that i dont have.