I don't have kids and I'm way out of that age range myself, but I read a lot of middle-grade / YA books and spend time on forums/websites with teenage fans, so...
Anything for kids by Rick Riordan - has pretty much already been mentioned (I'd say the original Percy Jackson series is aimed at slightly younger readers than Heroes of Olympus, but if a 10-year-old starts with PJ, there shouldn't be any issues with continuing with HoO). Liked by both boys and girls.
Skulduggery Pleasant by Derek Landy - the first five books have 9+ as suggested age on the back, the most recent ones have been 11+ but I'd say it'll depend on the child as they can get a bit gory at times. Liked by both boys and girls.
Boys 12+ seem to like anything by Darren Shan (Cirque du Freak, Demonata, Zom-B).
Mid-teens and older (15+) seem keen on anything by John Green. Girls and boys both.
Cassandra Clare's Mortal Instruments (and her other series) - mostly girls but also a surprising (to me) amount of boys like these. 13+, I'd say.
Alex Rider by Anthony Horowitz and Artemis Fowl by Eoin Colfer are mentioned a lot - Alex Rider probably mostly (but not exclusively) by boys, Artemis Fowl by both. I can't really tell what the lower age range would be for those, 10-ish?
A Series of Unfortunate Events by Lemony Snicket - boys and girls, 10+.
A lot of the above-mentioned books have quite a bit of humour in them.