Whom do I contact for a packing slip or an invoice?

Contact the Retailer where the product was originally purchased.

Best Buy
Web site: http://www.bestbuy.com/
For round-the-clock assistance, call Customer Care at:
(888) BEST BUY (888-237-8289).

CompUSA
Web site: http://www.compusa.com/
Customer Service: 1-800-COMPUSA (266-7872)
Email: http://www.compusa.com/contact/contact.asp?type=sales_support

Costco
Web site: http://www.costco.com
Customer Service: 1-800-955-2292
Email: https://www.costco.com/CustomerService/EmailUs.aspx?secure=1

Good Guys
Web site: http://www.goodguys.com/
Customer Service Dept.: (888) 937-7004
7:00 A.M. to 7:00 P.M. (Pacific time) 7 Days a Week

Micro Center
Web site: http://www.microcenter.com/
Customer Service.: 1-800-634-3478
Email: csrs@microcenterorder.com

Office Depot
Web site: http://www.officedepot.com/
Customer Service: 1-800-GO-DEPOT (1-800-463-3768), 24 hours a day, 7 days a week.
Email: http://www.officedepot.com/customerservice/input.do