[bestgenpower]

I'm not sure what you mean by visa renewal.
this recent thread has some info on visa runs (if you don't need a visa for a visa-free 30-day stay). that should take you to Cambodia. I'm sure plenty of travel agencies in Pattaya specialise at making arrangements for the least hassle-free trip possible.
http://www.thailandqa.com/forum/showthread.php?t=8834

if you want to extend an existing 2-month visa for a 3rd month, go to the local Immigration Office.
if you need a new 2-month tourist visa, the least difficult is probably Vientiane, Laos.