Playful is "a one-day conference all about games, play, design, interaction, behaviour and everything else that comes from playing about."
This year's topic is "Playing with Form". It's also not the cheapest of conferences at around £80, but last year was well worth it with great talks and all kinds of speakers. It usually sells out quickly.
If you want to go, please buy a ticket on their site, rsvp-ing here won't do anything.