Hi Kate, Ive just turned 18 and my favourite books were::
the Adrian Mole books (though not too keen on their covers).
Feeling sorry for celia & Finding cassie crazy both by Jaclyn Moriarty - liked their front covers, oh and also she's brought out a new book called Becoming bindy mackenzie, all her covers are bright and eye catching, i know it bad but i always tend to pick books out by there covers!
The georgia nicholson books by Louise Rennison, again they have bright colourful covers.
My mind's gone blank now!!
Hope this might help a bit!! ill try think of some more!
Em x