My 4yo son loved anything to do with cars - matchbox, hot wheels, Disney Cars (Lightning McQueen, etc), or big trucks. He also really liked board games for his 3rd birthday, especially Candy Land, Chutes & Ladders, and Sequence for Kids.
Also, I sell Discovery Toys, a home-based company not available in stores. We have some amazing products for three year olds that are not only fun, but also educational (though the kids don't realize it!!) and they all come with a lifetime warranty! A couple of my favorite products are perfect for preschool-aged boys - and I can honestly say my son and his friends all love them (as do the other boys I've sold them to).
You can view all the products at http://www.discoverytoyslink.com/karenchao If you order today, you'll have them by the end of next week. A few of my favorites:
MotorWorks - the company's # 1 selling toy! Children use a battery-powered screwdriver to build a car, motorcycle, and an airplane. They can take them apart and put them together over and over.
MarbleWorks is also great, though it does use regular sized marbles, so it's not good for a kid who still puts things in his mouth. Connect colorful tubes, chutes, ramps and bases in different ways to create an infinite number of racetracks.
Block It - a set of 40 wooden blocks with different shapes, colors and textures, perfect for building castles or anything else his imagination comes up with
PlayTown Series - choose from either a restaurant, a pet hospital, or a school. Each wooden playset comes with two characters and about a dozen accessories for pretend play and a chance to re-enact real life situations
Zingo - a fun bingo-style game to build picture and word recognition skills (adults really enjoy playing this one too, so it's a great family game)
ABSeas - another letter recognition game, this one uses magnetic fishing poles and can later be used for basic spelling too
I hope you find something you love. Please consider these toys - they really are high quality, fun, and with the lifetime warranty, they are better than anything you can get at Toys R Us.
K.