Neth, as an official Blue response, says Blizzard is working on it, and the best thing to do is simply report the spammer through the usual channels. Works for her, but it lacks the instant revenge factor, and even if the GM deletes the offending account, most of the spammers use free accounts to do their dirty work anyway. Some other players suggest doing a little vigilante work (feels better, I agree, but could probably get you in trouble eventually). There's always the option of leaving chat (which I'm doing more and more lately), but then there's the chance you might miss out on something important).
In the end, we go back to Polonaise for what seems like the best solution so far: allow players the ability to turn off messages from every character below level 10, unless whitelisted on your friends list. At the very least, it would make spammers play for two hours before running spam messages, which might push their investment over the top of profitability. In fact, I'd go as far as to suggest giving players the option to ignore all messages that don't come from friends or guildies. I doubt that'll ever happen (Blizzard wants this to be a social game, and shutting everyone out goes against that), but it's a definite solution to the problem of seeing spam all the time.