Here is a full guide on how to flash back to stock!
In this video I cover:
-JPU – Full ODIN flash
-JPY – PDA Only flash via ODIN – to make it able to connect to Kies
-JVO (latest as of 17/06/11) gingerbread ROM via Kies

Remember to wipe the INT SD and Factory reset before you send it in!

Download stock firmware from here

The select Samsung I9000.

You have to register and once you download the files you will be prompted to enter a password. It is mentioned on http://www.samfirmware.com/ however here are the 2 variations of passwords you will need to extract the file to your PC:
## Password is = samfirmware.com
# Password is = samsung-firmwares.com

Enjoy!
–TotallydubbedHD