http://www.supercook.com/ is a front-end to allrecipes.com
Not sure if it wasn't working when I tried it, but I entered 'capsicum' and it showed no recipes. What I envisaged is a site that would randomly pick a common ingredient (rice, potato, coconut milk) and confirm that the visitor had it at hand. Then go from there, rather than starting by having them name something they had.
CookThing seems similar I guess, but not quite the same.