I haven't looked for a bit (and its blocked at work) but I have bought several PCs and laptops from HP on their E-bay site - HP Renew.
Usually discontinued models (it was okay last week then) or stuff that has been returned. All come with a waranty and you can pick up some really cheap PCs.
To be quite honest, 90% of people have a PC that is more than powerful enough for their needs so you don't always need the latest spec. Don't spend money you don't need to if all you are going to do is surf the net and write the odd e-mail.