>I have a site that one day will have a page listed #1, >a couple of days later that page has completely disappered, >and then a few days later the page is back again at #1. >Are they rotating data bases? They could have some sort of randomizer going that gives search results in variable order when the relevancy rankings are similar. Or, something that rotates the order of the search results so the site rises (or sinks) with each search request. It wouldn't be difficult to program - just add fields that give the date and ranking and use them in the fetch routine. I've seem something similar in a database (to avoid the alphabetical bias they randomized their results).
Try this experiment - check your ranking about once an hour for a while, being sure to clear your cache between checks, and save the search results page. Do that for a week and see if the other top sites are yo-yoing too. If they are, there's little you can do on your end about the search engine, so you'll have to work on content and reciprocal links to build traffic.