assuming you'll NEVER use those other cards again, the arguments for WHY to keep them are:
1 older age of accounts
2 sufficient # of trade lines
3 mix of tradelines (store cards and national credit accounts)
4 even if paying off every month, the utilization % of credit will be lower than if you just have 1 card you use and payoff monthly....
5 if you like another card from your old issuer, you may be able to easily ask for a product switch, or apply the old line of credit to the new one
6 costs nothing to keep them (assuming they have no annual fees)
reasons NOT to keep them
1 annual fees (if they have any, most dont)...if they do, get rid of em
2 potential someone can get the # and charge (pretty hard if you destroy the cards, and most issuers have 100% fraud protection)
http://www.sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/2002/01/27/BU146130.DTL&type=business
edit: and taken from the fatwallet finance forums,
"According to FICO's brochure:
http://www.myfico.com/Offers/Brochure/Credit_Scoring_booklet_2002.pdf it will NOT help you to close out old accounts. Also, it doesn't help to open up accounts just to have "more accounts" or "more available credit"."
Credit Card FAQ:
http://www.fatwallet.com/forums/messageview.php?catid=52&threadid=158558