In spite of sync is disabled, sync icon is shown in notification bar forever!
I recently had the same issue - I have an old Samsung Galaxy S with Android 2.3.6.  I think somehow an app got updated when I was on WiFi, but I didn't know what it was. I noticed a "sync" icon appeared and would not go away. 

I finally realized I could go to Settings &rarr; Applications &rarr; Battery Use, and find out that YouTube was the culprit.

Then I could force stop that app and the icon went away, but it came back after a reboot, so I also uninstalled YouTube app updates.