DS just had his 5th and here are the best gifts:
A grabber (one of those extension grabber thingies...he loves this!)
A human powered flashlight (the ones you have to pump)
A lava lamp (great night light I have to say)
An encycolpedia on Dinosaurs (he adores this!)
A make your own planetarium kit
Hotwheels
Thomas the Tank little golden book
Several TTT&F engines and track bits
He is not really into the legos and he got a wee kit (which I highly suspect came out of a Burger King kids meal, but whatever)...the pieces have scattered to the four winds destined to find the tender inner sole of my husband's foot one dark night when ds cries out for water or something. He also got playdoh and when I discover the parent who gave my child this without telling me I will send them my carpet cleaning bill.

(they don't do gift opening time here, the kids just open as the guests arrive, and ds was given this gem by one of the guests as I was preparing the snacks and before you can say "Steam cleaner" all three tubs had been dumped and mashed into his carpet and his quilt into an unrecognizable smear of salty neon artsiness)....not my favorite gift as the mom.
I for one do not think you could go wrong with a good book or things with wheels.