Ultimately its what ever the client request but I keep the original art work for future changes. As outlined on my site the client usually recieves the .eps file, jpg, and tiff. The client at any point can request a different format to be delivered.
I believe the most important piece is to communicate what the client will recieve. Please check out what other graphic designers do by clicking on this link. Link to discussion board If you are a designer please let me know what do you normally provide your clients with?