You can play a Flash demo of the upcoming Puzzle Quest: Galactrix right here. It's definitely a lot like Puzzle Quest. I'm not sure about the cascading pattern when you remove gems...it's a bit confusing. And I cannot figure out what the purple and silver gems do. But it sure looks like it's gonna be fun!!
(EDIT: Kotaku reports that a more robust PC demo is also available. I haven't tried it.)