LOL, true enough. Let me re-state - if the client asked you to complete a form W-9, then most likely you will receive a 1099-Misc.
http://www.irs.gov/Businesses/Small-Businesses-&-Self-Employed/Forms-and-Associated-Taxes-for-Independent-Contractors
Otherwise, you will have to rely on your own documentation, such as any invoices you sent them, payments received, etc.