We d20 Modern fans have sure been lucky - there is a lot of great stuff from WotC and other publishers, print and PDF, that it's really hard to pick a favorite.
Stan!'s Heartless series is probably the best of the free adventures so far.
James Wyatt is a much-underrated writer and he seems to be doing well in Bullet Points. I'll be interested to see this d20 Modern project that he's working on, whatever it is.