I have two, sweet little brothers, ages 8 and 9. Although adorable and irresistible they have one ginormous flaw: they have extremely specific ideas of what constitutes "cool" handknits. They love knowing I knit something for them, but they are very particular about what they'll wear.
Here are just a few things I know they'd love:
Stegosaurus Hat

Ok, this one is a cheat: I designed it two years ago as a Christmas gift. Actually, D helped me design it: he drew a picture of his ideal hat and this is how it turned out!
Fingerless gloves

Both the boys want a set of fingerless gloves for recess. Leafy would be perfect for a pair (shortened for the shorter hands, of course!)
The Batman Logo chart and the Transformers Logo chart can be added to a basic hat or made into a simple patch for their backpack. They'd look great on a full-fledged sweater, but these boys grow to fast for a handknit of that size!
Although, at 8 & 9, they're a little too young for it, the Jayne Cobb Hat

For the extremely particular amongst your boys, this is Ribbed Beanie

What do you knit for the boys in your life?
And if you're afraid of what your boys might buy you, may I suggest pointing them towards a Blonde Chicken Boutique Gift Certificate?