Trenchbroom.
I used to make maps using Worldcraft (1.06 or whatever it was). I never completed those maps actually, I got somewhat far into a few of them.
TB is fun to map with. I used to have a lot of fun mapping with UED back in the day, I used to find that I would get so far and I couldn't make out what was happening on the grid, the beauty of mapping with TB is you never need to look at the ridiculous mess you made of the grid.