A while ago I started collecting old oil paintings of flowers after I had seen a lovely eclectic collection in a magazine. When grouped together it doesn't really matter what the individual paintings are like, as it's the overall effect which makes the statement. Sourcing floral paintings from car boot sales and eBay has now become a minor obsession of mine.
I also spotted the visual merchandisers Anthropologie and Fishs Eddy in New York had also used this idea, using old portraits.
Oh dear, I feel a new collection coming on!