The best place to find these games would be a local game traders club. Another option would be to look on lists and online to see if anyone is selling theirs also.
eBay is the best place to find games for the Nintendo 64.
Ebay
If you like football games go with madden'10
at a place like 'fusion odessy' or 'trade a game' basically your local used video game or nerd store.
about 60 $ the best place to buy them is here they also have a lot of games http://www.lukiegames.com/nintendo-64-n64-systems.html
Ebay
Gamestop or Best Buy.
Madden 11 is going to be the best madden game. As the years go on they might make a madden 3000.
Many sites have Nintendo DS games at a low price. Walmart, Target, K-Mart, Amazon, Best Buy, and Gamestop all stock Nintendo DS games of varying prices.
It is one of the best games I have ever played
The Legend of Zelda: Phantom Hourglass
that would depend on what games you like