Autogallery is fine as long as you don't mind the link at the bottom...
Is the site a high traffic site?
Because if it is you'll need something more robust and less demanding on the server, something written in C is the cream. There are allot of free tgp scripts you can run but they will skim 1% (they say 1%) from your traffic.
A little heads up on the traffic density and if you're running trades would help narrow the field down a little.
