Is there any mmorpg besides runescape, and world of warcraft that has a big trading scene for ingame currency to IRL currency?
Go to http://www.playerauctions.com/ and check the featured games on the side bar. Those are the rpg's that have the biggest market for gold/irl cash
Mabinogi used to be... But I haven't played it in a long time, so not sure anymore... But I bought/sold gold for it for awhile... Made about $100 in 2 days. I'm sure you can make a lot more than 100 on RS/WoW, but you'll probably also be more serious about it than I was... However, just be prepared if you're buying/selling Mabi gold, it'll be impossible to NOT do business with some shady Asia-based gold sellers unless you can find some Mabi players on here - Haven't seen any myself though.
The WoW market is getting smaller and smaller everyday. Other games that are still relevant in the MMO scene are Guildwars 2 and Archeage.