My brother-in-law will be 12 this coming spring, and his parents are looking to get him a nice bike... he's currently on a 24" wheeled full suspension catalogue BSO with cable disc brakes.
I've stepped in as "the bike police" and told them that for money - under £150 ideally - they'd be better off getting him a secondhand hardtail with v-brakes (it'll teach him how to ride properly, less to go wrong, lighter etc.) and letting me set it up for him.
So that's the brief - a small (13-14") framed complete hardtail bike with full gearing, 26" wheels, rim brakes and decent front suspension. Under £150, as we need a few quid to 'pimp' the bike a little for him. Bear in mind that by his birthday, he'll probably be about 5'3", probably a fair bit taller by this time next year
Posted in the pre 1998 section too.