I got a link from a friend a while agi to The Museum of Bad Art in Massachusetts, USA. It's not a joke, apparently, but a real place. Their online collection is well worth browsing through (pace yourself; a little goes a long way here) and if I ever happen to head in that direction I'd be delighted to pay the museum a visit. More background and other information at the Wikipedia page.
For some reason or other I'm reminded of Skissernas Museum - The Museum of Sketches - in Lund, Sweden. They collect sketches, pre-studies and models of monumental public artworks - and in some cases sketches of proposed works that thankfully were never made at full scale and inflicted on an unsuspecting audience. Like most museum websites, there's precious few examples to view; I wish more places would follow MOBA's example above and actually give visitors a taste of what they have to offer.