if you click on the shopping section in the blue strip under the mumsnet logo there is a company called easy2name. I've used them and they are good and you get a discount for going through mumsnet. However I will say by year 1 I'd resorted to easy peasy laundry marker and just write ds name on, very quick and painless when doing a whole lot of new uniform.
I have got the fab and funky ones from easy2name through mumsnet (you get a 10% discount). I have washed the clothes once and they are still on so far - cant vouch for how good they are just yet as this is the first time I have used them.