Mutants & Masterminds and its Freedom City sourcebook top my list. Excellent art and design that uses color to best effect (unlike, say, Bastion, who print in color but often get crappy art; guess what, crappy art in color is still crappy!)
Avatar's and Witch's Handbook, also from GR, have some great b+w art. Fiend books too.
I also like d20 CoC and OA from WotC. Wizards books look really good when they try (which they clearly don't on the splatbooks, which are shockingly mediocre when you consider the quality of artist WotC has on tap).
Privateer stuff has very nice art but their design is too busy. I can't imagine ever actually using the Iron Kingdoms character sheet, for instance.