Well the best game for N64 was Zelda The Orcarina of Time was THE best game ever, I still think it's the best console game (Not very much of a console person here), and yeah it would probably be a bit slow on the iPod Touch...
Here is a thread that says all the possible emulators: http://www.ifans.com/forums/showthread.php?t=12264
I think there is a program that emulates sega games on the gba or something and it works with gpSPhone
I think it would be interesting to see the atari 2600. You control the joystick by moving your finger.
Your just asking for a flame war. Anyways, Atari, Sega Genisis and a sslow N64 emulator would be cool. These emulators will probably come out eventually, we just have to wait..patiently.
No offense, but there is no need to open up a 6 month old + thread by asking a question that has been answered dozens of times not only around around the forums but in a thread that is on the front page of the Emulators section of the forums.
a nintendo ds emulator would b awesome ive got one on my computer with workin games but its probably not possible on an ipod touch