I've recently started investing in large numbers of NNNNN.com's. There are not that many left, less than 20% of the total amount, which itself is only 100,000, much less than the 450,000+ LLLL.com's. And these domains get traffic, even completely random numbers get small numbers showing up regularly. I think these are the next net real estate to be sold out. In addition to zip codes (all US are taken but foreign postal codes in large cities are available), there are good number combinations with repeating numbers, sequences. There are also NNNNN.com's that spell words, that are parts numbers, that are lucky numbers in China, etc. Lots of possibilities.