Pokemon. I've had almost every game that was released from Pokemon Red and Blue to Black 2 and White 2 and Pokemon TCG (Too bad it got stuck with GBC and the sequel isn't available in English. I'd love to see a TCG available for the newer handheld devices.)
Aside from that I think the Shin Megami Tensei franchise is awesome. I'm currently hooked up with Persona 4. I freaking love this stuff!