I thought I would start this thread, as it is supplementary to the one on blog monetisation. That thread seemed to focus solely on the income aspect, but there is also a capital aspect. Often it is possible to sell a name for more than the price justified by the income you have built. Also if the buyer has a different use for the name, you may be able to preserve part of the income. If there is any interest, then I will run this thread with http://adaptcars.com/ - the name I registered during part of the discussion in the blog income thread. The name has cost $8.49 so far, and that is for a year's registration. The target is to sell it for around £150 at some time in the next couple of years. In the mean time, I'll sort out some hosting to cover the costs and make a few dollars extra. It will take me a few days to sort the hosting, as I want to use the multi-site feature in WordPress to manage these names.
You will not that it is a .com, and if you are looking for capital gain, then .com is the only extension worth considering imho.