A common deadbolt works. Put a piece of 1x4 under it and it fits just right. Goes in quick if you don't punch the hole for the outside part. I just wanted to get rid of the emergency hardware, mostly because it was pretty much unlockable, and stuck this in for a 'quickie' until I could find something else.
Filled the hole where the original latch went through the door with one of those things that you use on the fourth hole of a kitchen sink when you don't install a spray hose, chrome side out and added a handle from Ace to pull it shut with. The only mod you have to make is take the back off the lock and flip the sliding part over so that it's beveled the right way, because from the lock's point of view the door closes backward.
RV latches work good too. I replaced the deadbolt with one.
It was about 30 bucks at http://www.rvsurplussalvage.com/
, they have a few different kinds.
I got a locking T-handle latch for my engine door here