1. Without a reflash, I'd say the best intake is the AFE (12 hp dyno proven without a tune)... the
K&N (about 7 hp) comes in second in my book.
2. Doug at Bamachips has dyno'd a 4hp/6tq increase with a pulley. It would be one of the last mods I'd consider when I'm trying to sqeeze every last bit of hp out of her.
3. Some mods to consider would be opening up the exhaust with a more free flowing muffler... either a single axle-back like the Ford Racing (
Borla), JBA,
Magnaflow or GT take-off. Or, going for a cat-back dual system, like the JBA or Magnaflow. You'll probably get around 10 hp with any of these. Plus, a really nice, throaty sound. Of course, with a dual, you'll have to either notch your bumper for the driver side pipe or get a bumper for a GT. As cost is a factor, I'd probably go with the
Borla single or the single GT take-off (very inexpensive, but sounds nice!).
Truthfully, an SCT X-cal 2 (or the original) with a tune from Doug at Bamachips or Lideo at Alternative Auto (there's a few other good tuners out there) would be the best bang for buck on an auto. It makes the car drive like it should have from the factory. After I used one of Doug's tunes, even the 87 octane tune, I could easily spin the tires at half-throttle from a dead stop. Combine this with an intake, like the C&L or Tunable Induction, and your car will be a different beast!
If you're really set on keeping the computer tune stock, stick with an AFE intake and any of the exhaust mods listed above.
Good luck!