Usually its not actually warped rotors in 99% of cases. Its from the junk stock pads, when they get hot they leave pad residue on the rotor. If you get them hot and then hold the brakes at a stop (such as at a light or something after driving hard) it will leave residue just in one spot. You can usually even see this on the rotor. Try bedding the pads in, usually when I change just pads I just take some steel wool or sandpaper to the old rotor to get as much pad material off before bedding the new pads in.
Stoptech had a good article about this. It would take a lot to actually warp the rotors, the stock front rotors are pretty decent.
Finally, a voice of reason. Normal driving will not warp rotors. Dragging the brakes or going easy on them creates pad deposits in the rotors that create an uneven braking surface that causes the shaking feeling.
If you change your pads, turn the rotors and bed the pads in. If you replace the rotors, bed the pads in.
Bedding In Brake Pads:
Find a nice stretch of road some where you can not impede the flow of traffic or break any traffic laws. I am not to be held liable for the practice of this in an unlawful manner.
Accelerate to 60MPH and apply heavy and even pressure to the brake pedal until you slow to 5MPH. Accelerate back to 60MPH and repeat this process 6-7 times.
Drive around somewhere to let the brakes cool a bit. Do not use them. Drive at a constant speed for a few minutes.
Repeat the accelerate then brake procedure one more time. At the end of this cycle drive around for a few more minutes and then park by slowing and using the emergency/parking brake. You want to avoid having the brake pads make contact with the rotors as it will create deposits, which is what we are trying to avoid by doing this process.
You can help to keep things scrubbed clean by occasionally really hitting the brakes. This will help to momentarily heat things up and even out the deposits. Or, buy something other than stock pads.
Things I have done to my brakes
Hot spotted the rears - after a spirited trip up and over and up and over and up and over Rt211 with some other enthusiasts, I stopped and parked for a bit. Soon after, I noticed a weird speed dependent noise from the rear. I found a black spot the same size and shape of the pads on the rear rotors. This was remedied by turning the rotors and removing the bad metal.
Scored the brake rotors - waited too long to order and replace my rears (come to think of it, I never heard the squeelers) and suddenly I was met with a metal grinding noise of pad plate meeting rotor metal. This ended up creating rings in my rotor. Again, not the best thing in the world, and this was remedied by turning the rotors. Come to think of it, I might have discovered both of these issues at the same time.