A number of useful spies?

[Cindy C.]

No: HPFGUIDX 28781

Here's a quick question, but if it has been discussed extensively 
before, just point me in that general direction and I'll go off and 
have a good read about it.

The conventional wisdom is that Snape is a spy for Dumbledore.  But 
in PoA, "The Marauder's Map", Fudge says "Not many people are aware 
that the Potters knew You-Know-Who was after them.  Dumbledore, who 
was of course working tirelessly against You-Know-Who, had a number 
of useful spies."

I wonder who else might be one of Dumbledore's "number of" useful 
spies, as "a number" would indicate to me that there should be at 
least three.  It seems that a spy would be most useful if he/she 
could pose as a DE or was otherwise close to a DE.  Could Pettigrew 
have convinced Dumbledore that he was spying on Voldemort, when in 
fact Pettigrew was (as we now know) really spying on Dumbledore?  

Could Narcissus Malfoy be a spy, leaking pillow talk to Dumbledore?  
Ludo Bagman?  Any other possibilities?

Cindy