I\'ve searched around for an hour, both on Stack Overflow and elsewhere. Alas! Please help. Vim\'s omnicompletion just doesn\'t work.
I have Vim 7.
Since you were prudent and made certain your code is reachable by the PYTHONPATH, per codeape's suggestion, is there a possibility that you are running into the import bug for Vim Python omni-complete? This bug still exists as of Vim 7.2.245.
Essentially, if any import statement fails in the file you are working in, regardless of whether it's wrapped in a Try-Except clause, it will completely break omni-completion. It should be fairly easy to check for this, since most imports occur at the very beginning of the file.
If you do decide that this bug is the cause of your troubles, your options include:
import statements that fail