I've been working on my sprint form lately and find that above a certain cadence I tend to bounce a bit.
What can I do in order not to bounce so much? If I try to actively think about what I'm doing, then it tends not to be as bad. However, I'm wondering if there are some good drills I can do on a trainer or rollers to help with this.

Are you doing these seated?

Most of the time, yes. Although I will sometimes try standing sprints or ones where I drop my hip down towards the top tube to power down and then stand for a few pedal strokes and then sit.

Yeah...get the Sprint workout from Trainright.com...plenty of drills and work on technique.

When sprinting in the drops, shoulders have to be behind your hands and pull up withthe hand on the side where you are pushing down...and if you are bouncing, drop down a gear..but the DVD is good. Specific drills to get better at sprinting.

Rollers.

Start out just riding the rollers, then gradually work on going faster and doing sprints on them. You'll eventually be able to get wicked high leg speed while seated without bouncing (see the thread in the track forum about how there were a million sets of rollers and 2 stationary trainers at track world cup).

Arnie Baker recommends doing high-cadence intervals to train neuromuscular fitness. Here are the specifics:

Duration: 2-10 minutes
Effort: 75-85%
Gear: easy
Cadence: 110-150
Recovery: 2-5 minutes
Repetitions: 1-10

Note that these are done in an easy gear. When I do them, I ramp up the cadence gradually. If you can spin an easy gear at a high cadence, you'll have an easier time staying smooth during sprints.

Couple of accelleration drills from my coach, similar to what Terry has provided from Baker, you can do them on the trainer or on the road:

Ride for 1 min at a comfortable cadence at an easy pace. Easy
Back off gear 1 cog at same intensity and ride for 1-2 min,
then back off another cog, keep downshifting until you
bounce. Repeat this twice during the workout.

Ride for 1 min at a comfortable cadence at an easy pace. . Easy
Back off gear 1 cog at same intensity and ride for 1-2 min,
then back off another cog, keep downshifting until you
bounce. Repeat this twice during the workout.

If you're seated it's really not a sprint per se, more like answering an attack or bridging a short gap. True sprints are off the saddle.

From the two pros I've worked with, they both start their sprint at their usual cadence, then ramp up to around 120-130 RPM, shifting one gear as they spin out of the point where they are making effective power.

We go out and do this in the morning or at lunch after a warm up, rolling off from 20 MPH or so, concentrating on form (loose upper body, breathing, smooth shifts just before the top of the pedal stroke).

The bounce either means you're tapped out or are pedalling a bit in squares.

Definitely worth working on, the improvements I made from practice paid off with three sprint wins at roadraces for me last year, and one narrow miss.

Spin-up drills on downhills really help. When you crest a hill, don't shift up, but stay in the low-gear. Then smoothly accelerate down the hill by pedaling in circles. Go right up to the point where you're just about to bounce and hold it. Then gently increase the cadence while staying smooth and round. You can really feel the change in form that has you transition between smooth & round vs. bouncing. The low-load of going downhill helps you keep the form and motion circular. Practice spinning up as fast as you can on the downhills. I can usually get up to 170-180rpms or so. Some of the track guys around here can hit 200-220rpms.

This exercise has a couple of benefits. First it develops the neural connections & timing with the muscles to contract at those speeds. And being smooth enough to spin that fast will pretty much ensure that you'll be smooth and efficient at the 115-130rpms that you'll actually be using in a sprint at the end of a race.