Elegant themes is quite possibly the most successful theme shop of all time. They have recently introduced flexible adaptive themes to keep up with the times. Trim is a meticulously crafted WordPress theme that features a clean layout and some nice reformatting of the text and panels as it shrinks down to smaller and smaller devices (like your iPhone of Android phone).
Their pricing model is one of the best – you get all of their themes for a yearly subscription of $39 (which you can cancel anytime).
I’m happy to see they they have gotten on the responsive bandwagon with their latest themes.