Thanks for all the recommendations guys!
Cougie - I'm looking at the SpiBelt website now, I love the size of the belt and the range of colours available. As long as I can be sure that it won't be a flapping nuisance I think that looks ideal, I might ask around my running buddies and see if anyone has a SpiBelt I can borrow for a training run.
HelenLiz - my old Nike tights had a pocket on the back (just under the waistband) which was perfect for holding tissues and gels. But I've now switched over to Adidas capris and NoBalls full length tights neither of which have pockets
Noanie and CaitlinBond - thank you for the feedback, it's good to hear back from other women about what works for our shape. It sounds like a silly consideration, but I know that if I get one that doesn't stay put I'll end up being so annoyed by it that I'll probably just chuck it by the side of the road somewhere! Also wondering about chafing if the belt moves a lot ... my next thread is probably going to be all about which is the best brand of runner's lube!
WRXMANIA - do you have the Nathan belt? It looks good, actually pretty similar to the SpiBelt (but a bit cheaper which is always good!) but I'm wondering if the clasps would be really secure?