Smelly cat, smelly cat, what are they feeding you?!
A couple of quick tips if your cat uses a litter tray and leaves less than pleasant odours:
Firstly, make sure you remove the offending objects as soon as possible!
Second though, which combats the ammonia smell from urine, is to sprinkle a little bicarbonate of soda (baking soda) into the tray. The soda absorbs the nasty niffs and keeps the tray a lot fresher smelling :)