Can anyone recommend a good (and good value) electric shaver for a teenage boy?

Braun Series 3 you can generally pick up the base model of within the £30 price bracket. It's good on sensitive skin and will still give a fairly close shave even if your technique isn't perfect. Unlike other brands they have kept the same parts for years so you can get a replacement cutting block later should he wish to stick with it for the long term, rather than finding it's useless and you need a whole new shaver because the blades are discontinued.

Philips get's a honorable mention with their rotary shavers, but having had one of them as my very first shaver I found it took a bit of practice to get a clean and close shave, and not have the discomfort of it pulling at some hairs. They are decent, but I quickly found I had a personal preference to foil shavers over rotary ones.

I'd personally avoid the likes of Remington and such. They aren't actually made by them and it's just cheap shavers with the brand name stuck on the box under license. They do a decent job to start with but don't tend to last.

So Braun definitely gets my recommendation. But if you can find a good deal it's sometimes worth spending a little extra for a better model (ProSkin - Better cutting block for an even more delicate shave and better ability to pick up hairs that lay flat. Rapid charge - Charge for a hour rather than 8. Pop-up trimmer - Good for going around the edges of things like sideburns when shaving to tidy and shape everything up)... Sometimes you can get these for around the £40 mark instead.

The Philips Oneblade is fantastic. I've had quite a few shavers but this is the best one I've found, not to mention the shaver itself is very affordable and the blade refills aren't too expensive. (edited)