asking for a top 5 in nes games is almost impossible, but I'll go through some of my most memorable ones (for various reasons) in no particular order
Kung Fu - 1st game I ever bought with my own money - when you get a dollar a week for allowance when you're 5, that's a freakin accomplishment...still own it too!
Ice Hockey - I loved loved loved playing as the czech's
Mega Man - most rented game ever (never bought it)
Rad Gravity - I think we just liked it because it was one of the rare games not liscenced by Nintendo (there's a good book on Nintendo's history called Game Over about how controlling the company was over 3rd parties - good read)
Super Mario 1 - I still play it every now and again and still have trouble beating it
Kid Icarus - any game where you can turn someone into an eggplant is ok in my book
Excitebike - fully customizeable tracks - awesome!