Unfortunately I don’t remember where or how I found this list but here is a big list of Twitter chats:

https://spreadsheets.google.com/ccc?key=0AhisaMy5TGiwcnVhejNHWnZlT3NvWFVPT3Q4NkIzQVE&hl=en

If they’re all even half as good as #lrnchat they’re well worth looking into.