I came across this site a while back when looking for places in Bangkok as I was working there for a short while...
http://www.thailongstay-tlm.com/intro.cfm
From what I recall there's some info on there about Pattaya but I guess the best thing to do is put a search in to google.com with the searchwords "pattaya rental apartment" or something similar. Pattaya used to be my favourite haunt, until I found Phuket !!
Good luck
Diz