Terrain! That extra ingredient to go along with your lovingly painted armies. You wouldn't want those little masterpieces to have to keep taking cover behind drink cans and stacks of books would you? Of course not!
Before heading to the links, let me say that I think the best terrain is that which you make yourself. It's going to be unique, have lots of character, and be CHEAP. Flip through some of the GW terrain books, or cruise the web looking for ideas. A good place to start could be Terrain from Junk.
But for when you have more money than time, there's a lot of options out on the marketplace these days. GW themselves are making a lot, but there are other options too if you're looking for something different.
Amera makes a wide range of vacuum-injected plastic terrain. It's extremely lightweight but still tough. I bought a number of their trench sections a while back, and have been extremely satisfied. As a bonus, if you have multiples of the same trench piece, they stack easily making storage a breeze.
CNC Workshop is an outfit in Australia putting out MDF terrain and terrain starters. I don't have any of their terrain yet, but have a number of their Troop Landers and can attest to the durability. At the top of their homepage you can select from a variety of currencies. Be sure to check for package deals!
Armorcast may not be making Titans anymore, but they still have a wide range of stuff to litter your battlefields with. Some cool vehicles too if you're looking for some alternatives to regular Marine or IG type tanks.
The Warstore carries a range of terrain products from different companies (and of course tons of figures too). A couple of examples:
- Ruined Columns from Battlefront/Gale Force 9. Heavy, and heavy duty. These sets come pre-painted and are ready for play right out of the box. They have other kits too, poke around!
- Pegasus has some good gothic styled buildings and ruins that fit right in with 40K.
- Sabol has some good looking mats to put out as tabletops that look pretty good for a reasonable price. You can see a review of the desert one at Table Top War.
So there's some things to get you started! Feel free to share your own favorite terrain links in the comments!
(image from http://www.cosmosmagazine.com/files/imagecache/news/files/20070413_alienplants.jpg)