Spy sapper: The Gentleman's Maneuver (dumb name)
+500% damage resistance to homewrecker / neon annihilator
-100% damage resistance to wrench
+25% building destroy time while engineer is alive
-25% building destroy time while engineer is dead
Spy cloak: The Stealth Watch (stupid name)
0.5 second cloak activation / deactivation delay
-10% cloak timer
-20% cloak gained from metal
Cannot be ignited by fire while cloaked - does not apply if wearer is not cloaked (doesn't affect mad milk, jarate, or any other types of damage)
Spy pistol: The Escape Artist (possibly decent name)
-10% damage penalty while disguised
-1 bullet clip size
Mini crits players while you are on fire / covered in liquid
Spy knife: Admin Abuse (clever name)
Insta-kill on all eG and eGO admins
I put a bit of thought into the first 3, but they're not perfect. Let me know if you like any of the ideas though

Also: eGO servers are the best