Unfortunately, it can be a long wait for the next PixelJunk game. Dylan Cuthbert told Parallaxed Game that the next game won't be unveiled for quite some time. In fact, nothing might be shown at next year's GDC show: "We can't talk about any of the future titles yet, we might not even show anything at GDC09, who knows! The next title isn't necessary based on the Dungeons prototype work as we develop several ideas simultaneously, finally going with the idea that has the most momentum."
It's going to be a long wait, but so long as their next game can match the addictive quality of Monsters and Eden, we're sure it'll be worth it. Stay tuned.
[Thanks, Adam T.!]