Motor Works from Discovery Toys has been my son's favorite Christmas present so far. My mom let him open this early and he has played with it for hours every day since he got it. At first I thought he would be frustrated and need a lot of help getting the pieces together, but he doesn't. He is able to do it all on his own, and rather quickly, too. What I like about this set is that it has it's own carrying case, making clean-up and transporting it easy. Also there are enough pieces that he can have all 3 vehicles constructed at the same time. Plus, this set has a drill that really works to take the screws in and out! He loves it!
Another similar set, this one is made by International Playthings in their TOMY devision. It is called Constructables and I found it on Amazon. The nice thing about this set is there are no screws, the pieces snap together. Another bonus with this set, it is more open-ended, meaning the child can create any vehicle using any of the pieces, there is no wrong or right way to put them together. It also comes with a motorized battery pack to make the vehicles go on their own. The downside to this set is that there are only enough pieces to have one vehicle built at a time. I love International Playthings, though, their toys are really durable!
Djeco, a French company, is the manufacturer of this Super Builder Set I found on Moolka's website. This set comes with instruction cards that look easy enough for a child to follow. I like this set because you get enough cars for a race! I love wooden toys and Djeco is a great brand.