Changing the brake pads is an easy job.  The following set of
instructions look intimidating, but are actually very straightforward.
Most dealers will charge US$100 to $200 to do this job, but the 
parts cost about US$25 and can be replaced in under an hour.

From: Thomas A. Yurick <designer@penn.com>:

Jack up front wheel. Remove wheel. Remove small bolt holding the
flexible brake line bracket on the strut tower. Looking at the caliper
assembly, there are two long sliding pins that the caliper slides back
and forth on. Each has a hex head on the back (away from you) side.
There is a place on the pin that you can fit a wrench and hold it while
you loosen the hex head bolt. Remove the bottom hex head bolt ONLY.
The caliper will now flip up off the rotor, rotating on the upper pin. Use
a piece of string to tie it in the raised position while you work. Make a
note of how the pads are installed. Look at the wear indicator on the
inside pad in particular. Now carefully remove the pads, the anti-squeal
shims and pad support plates (the little clip-like things at the top and
bottom on each pad), noting the way they are installed and their
sequence.  The pad support plates may be stuck to the calipers with
grime and crud. Gently pry them out. Clean any crud from the caliper in
the area where the pad support plates go. Clean up the pad support
plates. Reinstall the pad support plates in the same positions that they
were removed from.

You are not supposed to reuse the anti-squeal shims (the two thin plates
on the side of the pads) but I always do if they aren't damaged and I
never have a squealing problem. If your pads come with new ones, use
'em. Otherwise, use the old or get new ones from your Toyota dealer.

Sparingly apply disc brake grease (I use Never-Seize or equivalent)
to both sides of all of the anti-squeal shims. Install the anti-squeal 
shims, just as they were removed from the old pads, to the new pads.
Install the inner pad  into the pad support plates with the wear indicator
facing up. Install the outer pad. Remove a small amount of brake fluid
from the reservoir under the hood. Using a wooden hammer handle or 
other suitable non-marring tool, press in the caliper piston all the way.
If the piston is difficult to push back in, you can open the bleeder plug
on the caliper slightly and allow some fluid to escape while pushing it
in. Untie the caliper and swing it back down over the rotor. Hold the
pin with a wrench again and install the hex bolt and torque it to 20
ft/lb. Install the flexible brake line bracket and torque the bolt to 25
ft/lb. Repeat on the other wheel. Bleed all brakes starting with the
farthest from the master cylinder (right rear) and working to the
closest (left front). Fill the brake fluid reservoir to the full line.

From: Rav4 <Rav4@2929292.com>:

A couple of enhancements to the excellent instructions from Tom on 
brake pad replacement.
 
1.      The easiest was to compress the piston is to use a large "C" clamp
with a piece of wood across the piston face to distribute the force and
prevent pinching of the rubber boot.  Although you can put the adjustable
part of the clamp inside some pistons, it is not a good idea to put all the
force in the center area of the piston, so use a piece of wood, it is safer.

2.      With ABS systems, it is undesirable/dangerous to compress the 
piston back into place without relieving the back pressure.  In other 
words, it is important that you "crack the bleeder valve" when 
compressing the piston.  If you use a piece of clear tubing over the 
bleeder valve first (rising vertically above the caliper), as the fluid 
escapes, it goes into the tube and provides no ingress for air.  This 
way no air gets back into the caliper when you stop compressing the 
piston and you can safely tighten the bleeder valve without bleeding 
the whole system unless you really want to.