1.) Sell it 2.) Park it, if it receives some traffic. 3.) Develop it 4.) Do nothing, and let it expire
You add the following code to your footer (it will increase your PageRank - lol): <a href="http://www.nrglab.org">NRG Lab</a> Code (markup):
1. A PR5 domain can be very valuable to the right person so you might consider selling it. 2. Develop the site. But do something with it!
turn it into a directory. slap up phplinkdirectory - i believe there is a free version 2.0 i think avail - and keep adding backlinks. i'm sure you'd find a lot of business (and spam!) if you were advertising a free PR5 link directory.
Well. Not everyone buys a domain for the PR. In most cases it is existing traffic. Does the site get traffic?
Sit tight and everyone will laugh at you when it hits PR0 or at best PR2 at the next update unless you start developing it NOW.
If you can develop the domain into a financial blog, and monetize it with Google AdSense then thats your best option ~ or sell it someone who can handle the development of such domain in a way that does not make domain lose its backlinks and eventually lose of its pagerank status. So you choose.
The short answer is develop it, but how you do it is the longer, more difficult one. In the end you just have to work on it; if it's a PR5 it's because it has quite a few backlinks and must be generating some traffic. At the least you can put adsense on it and make a few bucks. If you've really got the time start writing content for it, add a forum, add user generated reviews, turn it into a social networking site, etc. - whatever you can dream up, but keep some fresh content on there.