Watts is irrelevant when buying speakers. Most speakers are 4-8 ohms. I
would go to a store and get some moderately priced aftermarket speakers made
for cars.

I had all the speakers in my 98 Camry replaced soon after purchasing the car
at an car audio shop. I got some high-end Boston Acoustics, but there are
other brands that are more moderately priced. Try Best Buy, Circuit City, or
other electronic retailers.

You will have replace both sides at the same time (or it will not sound
right), and it would help if you replaced those on the rear deck as well
(but not absolutely necessary).