I'm going to buy Linux Virtual Private Server, but I would like to compare offers that hosting companies have. I would like to compare servers memory, disk, bandwidth, cpu and price per month. So far I have found manually searching that godaddy.com has pretty good offers, but I would like to compare more hosting companies to get best offer.
SquareCompare offers a comparison service with a variety of comparison criteria (advertised with them while working for a VPS hosting company).
Note: "Virtual dedicated" isn't a common term (remember seeing it first over at Media Temple - it isn't accurate at all if the server resides on shared hardware) so you might get better results if you're asking about/searching for "virtual private server" comparison services.
I found site http://www.lowendbox.com/, its not comparison, but it has a lot of blog posts about very cheap VPS hosting.
You can try this list of Cheap VPS Hosting provider's list. They don't have any straight forward link to compare all the plans, but you still get a very good comparison of various known - unknown VPS providers.