I spent quite a bit of time mapping in Portal 1 right before the release of Portal 2. I learned a ton on the mechanics of mapping with Valves Hammer Editor and the structure of Portal maps. If you are a fan of custom Portal 1 maps or custom maps in general click the link below to check it out.
Thinkingwithportals.com is an awesome website with constant flow of custom maps coming in. Hopefully I will finish my Portal 2 map one of these days, been too busy!