Can I use a receptacle and switch for a dishwasher and garbage disposal?
If you're using 12/3 with ground, non-metallic sheathed cable from the panel to the outlet, you'll have no problem doing what you want.
Materials:

20 ampere double pole combination GFCI circuit breaker.
20 ampere duplex receptacle.
Length of 12/3 with ground non-metallic sheathed cable.
20 ampere single pole single throw switch.
2x single gang boxes.

Procedure:
Pull the cable

Install a length of 12/3 cable between the switch box and the receptacle box.
Install a length of 12/3 cable between the receptacle box and the service panel.

Install the switch

Connect the Bare/Green grounding conductor to the Green grounding screw on the switch.
Connect the Red ungrounded (hot) conductor to the common switching terminals on the switch.
Connect the Black ungrounded (hot) conductor to the switched terminal on the switch.
Use a twist-on wire connectors rated for use with a single 12 AWG conductor to cap off the grounded (neutral) conductor.
Tuck all the wires into the box, and mount the switch.

Install the receptacle

Clip the tab connecting the upper and lower receptacles on the ungrounded (hot) side of the duplex receptacle.
Connect the Bare/Green grounding conductor to the Green grounding screw on the receptacle, and to the Bare/Green grounding conductor from the cable to the switch.
Connect the White grounded (neutral) conductor from the feeder, to one of the grounded (neutral) screw terminals on the receptacle.
Connect the White grounded (neutral) conductor from the cable to the switch, to the other grounded (neutral) screw terminal on the receptacle.
Connect the Black ungrounded (hot) conductor from the feeder to one of the ungrounded (hot) screw terminals on the receptacle.
Connect the Black Ungrounded (hot) switched conductor from the cable to the switch, to the other ungrounded (hot) screw terminal on the receptacle.
Using a twist-on wire connector rated for use with two 12 AWG conductors, splice the two Red ungrounded (hot) conductors together.

Install the breaker

Terminate the Bare/Green grounding conductor to the grounding bus bar.
Install the breaker in the panel (make sure it is in the OFF position).
Terminate the White grounded (neutral) lead from the breaker to the neutral bus bar.
Connect the White grounded (neutral) conductor from the circuit to the neutral terminal of the breaker.
Connect the Black ungrounded (hot) conductor to one of the ungrounded (hot) terminals on the breaker.
Connect the Red ungrounded (hot) conductor to the other ungrounded (hot) terminal on the breaker.

Turn on and test the GFCI breaker

Switch the breaker to the ON position.
Press the TEST button on the breaker.
Switch the breaker back to the ON position.

If the breaker will not switch on, there is a ground-fault, the wiring is wrong, or the breaker is bad.  Detect and correct the fault, and reset the breaker.
tl;dr
Here is an image showing what the finished circuit should look like.

Click for larger view
NOTES:

If using metal boxes, make sure to bond them to the grounding system.
You can also use 12/2 with ground, but you might find that if both devices are run simultaneously, the breaker might trip.