A friend suggested adding a wooden train set to the list. I agree. I was planning to put it in my elementary toy recommendations, but after she mentioned it I realized my just turned 3 year old spends lots of time playing with ours. He can construct a simple track but really likes it when one of his older siblings builds an elaborate one with lots of hills.
Many wooden track sets are compatible with other sets. We started with a Melissa & Doug set I purchased on eBay. We've added lots of pieces from the Thomas & Friends set. I think Brio also works with these two. I like giving gifts that can be added to over the years. My mom gave Andrew a new accessory for his birthday on Monday.
When we first got our train, I wanted one of the nice train tables with built in storage drawers. I also wanted the track permanently fixed to the table. We couldn't afford a table at the time, so I just bought a big Rubbermaid tub to store it in. That was 5 years ago and it's still in the tub. I am SO glad we didn't attach it to anything. I think our children have enjoyed it MUCH more by being able to build a different track every time they play. It also allows me to be able to store it out of sight for awhile and bring it out again after a few months. (I just learned my friend, Kimberly, is offering her readers a chance to win a train table from Constructive Playthings. Check out her blog for your chance to win.)
A couple of obvious suggestions are baby dolls and cars/trucks. With 4 girls, we have acquired quite a collection of dolls, clothes and other accessories. We've especially enjoyed Bity Baby from the American Girl Company.
Can a little boy have too many cars and trucks? I'm sure you can at some point, but I've seen my big boys (ages 9 and 7) line up over 30 of them and have their own NASCAR race. We have a playmat from Discovery Toys that has a road drawn on it. It is made up of 9 different squares that can be put together in a multitude of different ways. My boys have played with this A LOT. I don't think DT sells this particular mat anymore, but you could search for it on eBay or perhaps find a similar product from Hearthsong.