I have a 6 year old boy. He is getting Lego, a football kit and a
Kindle if I find one cheap enough on Amazon. Plus books - have you thought about reference books? My son loves this maps book for example.
Other things that could work - magic trick box, scaletrix, globe, telescope, fishing pole, gardening set, toolbox.
Going out type stuff - we're going away in a Premier Inn type hotel to watch a show, just me and him, leaving his Dad and sister behind! Also - any sort of dinosaur/science type day out. I'm considering either Marvel Universe Live or seeing the Robot Wars show for his birthday.
Also, smaller giving ideas- a torch, character t shirts, pjs, Superhero costume, more(!) matchbox type cars, wallet, money box, book light, magnifying glass,
Hope that helps!