I've always considered "I can return to this game and replay it" to be the ultimate sign of a good game - if, even years after you've 100%'d it, you actually want to go back and play it again, it has clearly done something very right.
So with that said...
* I go back to most of the Mega Man series. Often. For the most part they're short games so it's not like it's a huge timesink to do so.
* See also the Final Fantasy series; although honest FFV, FFX, and FFX-2 are probably the ones I return to most now. I've come to really appreciate their gameplay.
* Oh, and the Metroid series. Mainly from Super Metroid on. (I'm so excited to get Fusion on 3DS)
* Dokapon Kingdom. Hell yeah.
* Valkyria Chronicles series. So many characters to use, such grandiose battles, so many ways you can challenge yourself...
* Growlanser Generations. Possibly my favourite SRPG of all time or something, I really don't know but I do know that I fucking love it and love replaying it. GL2 was the first game I replayed when I moved into my new apartment and I marathoned it in a day.
* Tales of Symphonia. 8D
* Games by Hideki Kamiya. You know... Viewtiful Joe, God Hand, Bayonetta, all that fun stuff. They're just so much fun.
* SUPER MONKEY BALL. That is all.
I'm sure there's way more but that's what I'm seeing just looking around me.