I'm biased but I'd go with custom American steel from IF, Seven, or Waterford. They are lightweight and the new stainless steel tubes don't rust. Also, Lynskey titanium frames are stiff (like aluminum) and light. I've seen some really good deals recently on these frames. A friend has one and it is an amazing piece of workmanship. I can't think of the name of the popular custom aluminum builder but you should check the framebuilders section for a builder from Oregon who is famous for aluminum custom builds. I also think Comotion builds aluminum frames.

If you are open to non-custom, you can probably get a good deal on a CAAD9 alum frame, the darling of BF. This frame is a bargain and the last of the US models are being phased out.