The JSON-API wiki page describes all the methods: http://www.bitcoin.org/wiki/doku.php?id=api
The wiki needs a good re-organization; anybody want to volunteer to revamp the Start page?
RE: comment and comment-to : they're stored in your wallet along with the transaction, but not sent over the network. The new gettransaction and listtransactions methods will return them (as "message" and "to").