In reply to TobyA:
The Islabike sizings are really accurate, so a good guide to see if one of their bikes fit. There's a lot of leeway in what kids will happily ride - my eldest has just turned 9 (average sized!) and raced a small Beinn20 all last year when most of the kids he was racing against were on 24 or 26 wheels. The wheels looked small but the bike fitted him perfectly with a really nice balanced position, rather than the saddle low, bars high struggle to get to grips with it style you often see. So don't feel the need to go up a wheel size just for the sake of it.
I actually started building him a 24" bike for last summer and (to my shame) have only just finished it. But to my relief I reckon he would have been too small for it last year. I would have gone for the Creig24 but couldn't really stomach the price, so put something together with an old frame off ebay and some donated parts, and probably more new parts than I intended
It definitely came out cheaper, but I pulled in quite a few favours in putting it together, particularly getting a mate to shorten the fork.
Here's what he looked like on the small Beinn20:
http://www.flickr.com/photos/jon_b/9874739295/
And here's the new ride:
http://www.flickr.com/photos/jon_b/13326270585/
It's really only just small enough for him I think. I can't think of many 26" frames I could get to fit him, maybe some of the smaller women's frames might do it. Once into adult frames it's the length that's the problem, so women's frames come out a bit better.
The Orbea's do look nice if you don't want a sus fork (and they are the biggest headache with 24" wheels). Scotts look nice too - and you see a lot of kids racing on those.