When Ol' Myrt recommends searching the scanned images of US Federal Census records online, I think of three places:
ANCESTRY.COM (fee-based to individuals, free to FHCs) To locate a FHC (Family History Center) near you, see: http://www.FamilySearch.org
HERITAGEQUESTONLINE.COM (fee-based, sold to libraries, not individuals) To locate a library near you see the growing list at http://eogen.com/HeritageQuestOnline
Yes, there is the free USGenWeb CENSUS PROJECT, but it isn't complete. See if your ancestors' localities are online by visiting http://www.UsGenWeb.com
Happy family tree climbing!
Your friend in genealogy.