i have an obsession with hello kitty, so when i lose weight and i feel good about myself, i will buy something small that is hello kitty to reward myself. i also love books and i find that when i lose a certain percentage of weight, usually 5% or 10% weight loss i will buy myself a new book or something hello kitty. it's ultimately up to you, if you really like something then buy yourself that... i like books and hello kitty stuff though because i can buy little things here and there, but when i lose my first 50 pounds, i might reward myself with something bigger.
-Stephanie