Depends what sort of game it is. If it''s an indoor BSP''ey engine, you could use Worldcraft and import it''s map format. If you''re making a terrain engine, you could just use Photoshop and import images for the heightfield. If it''s a more generic engine, you can always use MAX and import all the triangles and convert them to a more usable format (e.g. portalize them or BSPize them or whatever you want.)

It all depends on the structure your engine has. There''s no such thing as a generic level editor though.

War Worlds - A 3D Real-Time Strategy game in development.