well im sure you already know but the 2 most obvious would be anti virus or some type of medicine/illness site
dependingon what you would find more interesting/easiest to do whether you plan on selling it or to keep running it, all depend on what you should do with it
ie you cant run a medicine shop if you know nothing about medicine, in which case anti virus software would probably be best to do or vice versa, whereas if you plan on selling it then it would be best to develope a site which would get you more money and be easier to sell
The most easy to do is an antivirus review and information website like Tom said. Maybe could you have virus encyclopedia if you find good content. Maybe add some XML feeds about virus alerts. Nice name, great potential..
i think you can create a site where you will have many antivirus reviews with a voting system so that everyone can vote and in end of everyweek there will one popular antivirus (which had got maximum votes). Beside review you can give a link to download also.