I’ve had to refer some people to terrain building sites lately and have given them the classics.
Major General Tremorden Rederring’s Colonial-era Wargames Page.
This is one that I used to check in with all the time. Since it hasn’t been updated since June of 2006, it’s probably unlikely to change anytime soon. Which is a real shame as the General has a lot of good ideas. He’s mostly doing colonials but has some great information about ships, landships, and scenery. Of notable interest to the new True-Line-of-Site 40K is the Tabletop viewer and the Tall Grass section.
I just spent a bit of time going through it recently. I’m a bit sad about the lack of updates as it means that I probably won’t get to see the rules for the VictorianTech – a War of the Worlds-esque Battletech-type game.
From the Major General’s site I found the Terragenesis site – which is sadly no more. It has been replaced by the new Terragenesis site which has most of the old content on it. The Articles Index has a lot of good ideas and the forum is nice to visit. They do seem to be heavily into the contests lately, which is partly why I don’t frequent it as much as I used to. But I still recommend it to anyone about terrain projects.
A newer site that is also updated occasionally is the Hirst Arts tips section. Even though it mainly deals with using the Hirst Arts brick sets, there are a lot of useful info – like making a fence from epoxy glue, using water effects, and sci-fi ideas. I don't use any of the HirstArts products but they keep giving me ideas.
Another good site for inspiriation is the Necromundicon.
He's done a bunch of 40K and Mordheim stuff and has a good gothic feel to them. In addition, he has put up some rules for some games he made and terrain and bits for them. The Star Wars rules for the Galactic Heroes and the terrain to go with it are worth checking out.