I agree with Lisa on the Stencil Company's site. Nicely laid out, easy to find what you want. My suggestions:
I prefer soft white/pastel background for text (not bright white, not black)
Non-serif font
Little scrolling side to side (drives me crazy!)
A good search - If I can't find something quickly, I'm off to a different site
Menu that allows me to find what I want in as few clicks as possible
Clear and concise payment/shipping info
You don't say what your site is for, but if it is for fabric, I also like:
Ability to search by manufacture, designer, fabric line, color, theme, sale
Design board
color matcher
decent sized swatches
info on repeat distance
if stripe, is it parallel to selvedge or across width of fabric