Well if you're looking for people to watch play in game on the eGO servers, look for Sandman, TheZaw (never played against, but I guess you're good

), Jehuty (still plays on eGO servers) Frisky isn't too bad (I would say your great, but I dominated you as Heavy twice

) Cut Chem!st and myself all are pretty good spies. Remember these things...
1. Use the original watch.
2. You can disguise as anything, trust me. Disguises for the most part are for sentries and a good 4-5 seconds of hesitation. I guess disguising as Scout in a crowd isn't a good idea, but when you're far away it's fine.
3. Heights are your friend. Being above your targets has its advantages. Makes you harder to spy check, etc.
4. Try to change disguises only while cloaked. This removes that annoying smoke effect that can bring attention to you anywhere.
5. Always, always, always be disguised while you aren't shooting/stabbing. Use friendly disguises in friendly territory. Disguise as a friendly anything except Heavy.
6. Stab+Sap>Sap+Stab
7. Bad dispenser placement can save you. Just the other day I was playing on GoldRush, horrible dispenser placement allowed me to stab the engineer while standing safely behind the dispenser, redisguise and sap away.
8. Blend in. Don't look at the sentry you're about to sap all the time. React to enemy bullets and explosions. If somebody Spy checks you with a bullet weapon, act like nothing happened, while going towards a target. When sitting at an engineer base near a dispenser, do not... I repeat do not look, think about, think about looking at, breath on or anyways think about touching that sentry. Just sit there and act as though you're healing or getting more ammo. And then move in when the crowd is gone. Don't be that Spy who just runs up to an engineer base and saps like crazy, gets crit wrenched and the sappers are removed. It does nothing but make the engineer more suspicious.
9. Never use the same disguise twice in a row.
10. Switch weapons, walk around in base as a Sniper with a Kukri or Jarate/SMG. As a Demoman, carry your stickybomb launcher. Engineer, pistol or wrench will buy you extra time.
11. Because you should use the regular watch, always keep an eye out for ammo boxes/dropped weapons. You have to use your cloak wisely as it is your best weapon. Before you could recharge the cloak with ammo, it was a very short time to be invisible. I got used to that, and now moving across entire maps while cloaked is nothing short of very simple.
Those are some tips I tend to use

Have fun stabbing!