I'm looking for a generic level editor to flesh out some ideas on a 3rd person RPG type game. I mostly want the ability to create the maps with some reasonable degree of detail. I don't plan on using those maps directly in a game at this point. This is just to help me think through several ideas I have in the design process. What would be a good editor with a lot of goodies that would fit the bill? I'll pay up to about $50 or so if I have to but I really prefer a free editor if possible, as this is for brainstorming more than anything. Thanks!

Few ideas, not sure if they meet criteria for being 'generic':
Radiant
Hammer (WorldCraft)
MilkShape 3D

That's all I can think of at the moment. Happy hunting!

Drew is quite right!
Hammer is free and if you have any of the games that it supports, it means that you have access to literally thousands of textures. Then get textures packs on the Net and you are set.
You can do your prototypes maps in the editor and fly through them, even take screenshots (IIRC).
I know I did this quite a few times for Halflife, designing a nice natural looking map only to realise it couldn't even be compiled because it was just too complex for the engine [rolleyes]

QRadiant would be the equivalent, but for the Quake engine.

Then there is also the one for the unreal engine, of course.

Those map tools are very very good at doing what they are designed for, which is make levels for the games they target. If you want to do models, they might become a bit awkward (although vehicles/ships are pretty cool to make), but otherwise they are excellent, shielding you from the needless complexity of a "proper" 3D modeller. And they are free... [grin]

QuArk is free, and without any liscencing restrictions.

It can be found here. here.

Cartography Shop is sleeker, and only costs $49.

It's here.

GameSpace (~$300) is also able to be a level editor.

GameSpace and GameSpace Light.

GameSpace Light (some restrictions apply) is free, and can be obtained at that last url.

deled is generic and free (+license free). I believe it also exports to .3ds, .x, and some other formats.