[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.

[surefireinvest]

Do you mean Visa ?

A visa is only issued by Thai embassies so you would have to leave LOS to get one in Penang, Singapore, Vientianne or PhomPhen.

[ChrisGoldstein]

SK, depending on what visa you have, but the Thai immig. office in BKK would be your best bet,,very hard to give info as there is just so many different visas and each one is different.
If you now have a tourist visa and want to get a non O or something like that, then you will have to go outside and get it and come back, about the only thing you can do incountry is renew non immigrant visas.or add the 3 month to 60 day tourist visas. Hope that helps,you have my e addy if need be, use it