Cheap accessories are much nicer because they are less serious and you're not going to be that bothered if you lose them are you? As already mentioned the Johnny Loves Rosie catalogue is a good place for this, as is Accessorize (enquiries: 0171 313 3000) and Superdrug (branches nationwide) which can't be beat for naff kitsch value.
I asked Rosie Green, beauty writer at Elle what she thought of accessorising your hair. "It started a couple of seasons ago with the tiara thing,"she said. "It doesn't look weird anymore - it looks fun. Dolce e Gabbana had butterflies in the hair for summer and Galliano had little clips in the hair for his spring/summer show. It can really make an outfit if you dress your hair." Rosie did have some words of warning though: "If you overdo it you can end up looking like a Russian gymnast".
If, on the other hand, hair decoration is anathema to you, then that's okay too. Just make it very straight and flat and "skinny", exactly like the hairdos at Byblos and Prada. Well, that's sounds good, because to my mind, the best thing you can do to your hair is to wash it and brush it.