Yeah another vote for Fusion! I really like the funky graphical overlay for the Gamegear console. Before I discovered Fusion I used Gens for Mega Drive/Genesis games and found it to be very reliable also. Both emulators were very easy to set up with gamepads.
Also, I bought a 'USB Genesis Retroport' adapter which was a bit pricey but I love being able to use my original Mega Drive gamepad, feels so much more authentic!