If you dont want to use WED (or only a little), try these:

1) use Sivan's map editor
2) use code to create your map (e.g. generate terrain and grass through some loops and random()'s )
3) make your own editor (I would say worth the effort if it works like a typical game/map editor, as in it uses the game assests and has build in units/objects of your game, a more flexible editor is doable but takes more time)
4) not sure about this one, but I think there are several model/scene creating programs where you can create maps in which you can than import in WED. Not surehow good the workflow for this is though.
5) for tile based games/graphics, you can use a text/notepad file to create your map and load it ingame as a string/strings and generate world based on that.

2/3/5 (specially 3) offer extra possibilities for modders modding of your game.