Do you need a HDD? If possible, I would try to spend less on the case (~$25) and MB (~$50), and then spend that extra $50 on the GPU. I don't mind cheap cases though, and some people do.
Answer the sticky and we can answer your allocation question. The best way to allocate funds is according to your usage and needs. Without knowing those things, any answer is presumptuous. /shrug
generally speaking, your allocation looks fine, though. However, if this were a gaming machine, I'd drop the case down to $35, drop fans down to $5 (case should come with one, so you should need just one more), CPU down to $65 (dual core is fine for gaming), and put the saved cash towards a better vidcard (gaming is highly dependent on the gpu, hehe).
Less on ram, more on CPU. CPU is the single more important component on a computer. You should be able to get 2GB of ram for $40. With a $500 system, 2GB is enough, the rest is better spent elsewhere (more bang for your buck). Ram is one of those things where once you reach a certain point (2-3GB) for the majority of people, the performance gain really bottoms out.
Any day of the week I would take a high end CPU with lower end GPU/Memory than a lot of memory/gpu and a budget CPU.