What to consider:
This age group can be fairly opinionated about what they'd like for Christmas and peer pressure from the school playground might well influence their ideas of what's cool and what's not.
Classics (a new bike or scooter, a wooden castle or dolls' house, or board games) work just as well, if not better than, a particular year's 'must-have' toy. Think carefully about what will be played with for months and years and what will be cast aside in a week or two, no matter how much playground kudos it has.
If you're buying for someone else's child, bear in mind there's a huge variation in tastes among primary schoolers – some love fantasy toys, some prefer things which mimic real life, some are sports mad, others like nothing better than a bit of knitting or arts and craft, while yet more always appreciate the latest gadget.
If you're stuck for ideas and want to ensure you invest in a winning choice (and don't mind the lack of surprise when they unwrap it), ask the child or their parents for some hints.
With your own children, whether you go down the Christmas gift list route or not is personal preference – some people think it's a bit 'grabby', others like the way it means their kids get things they actually want and will play with. Amazon has a good, free wish list service.