The recently launched MPRIRE might offer a one stop solution to your online shopping. Enter say 'couch cover', the service will give you a few related options so you can narrow your choices and then list a number of items available. The company has a partnership with Yahoo, Overstock, Craigslist and EBay which might explain why the results coming up during my test searches where a little EBAY top heavy. I am sure that as time goes by they will widen the sources and the selection of items offered.
Otherwise the service seems well designed and is user friendly.