I (heart) Brian K. Vaughn.
Ex Machnia has been consistently excellent, heavy on the political drama and light on the superheroics, to the point where The Great Machine is a nice touch (and an intriguing mystery) but doesn't overwhelm the rest of the book. Vaughn has a lot of affection for New York City and, as a way-out-of-towner, it's interesting to read about the daily life and political wrangling of the city. For anyone interested in giving it a go but not quite sure about dropping cash on the trade, I second the recommendation of Issue 11. You'll get more out of it if you've been following the series, but it stands alone perfectly well and makes for a good sample of the series.
However, Y The Last Man is where Vaughn really shines. The title is literal: every male on the planet dies off, with the exception of our hero and his pet monkey. Seeing Vaughn explore the consequences of this disaster (as well as slowly investigating the cause of it) would be perfectly interesting in it's own right; however, add in top-notch characterization and a liberal dose of black humor and the book is positively gripping. The latest story line has me on tenterhooks eagerly awaiting the next issue.
Finally, if you've ever been a Marvel fan, Runaways is a must read. Don't get me wrong, the book is perfectly entertaining even if you're showing up to the party cold - it's hard to screw up a team book about teenagers battling supervillians who just happen to be their parents - but Vaughn's excellent use of Marvel continuity is what really makes the series for me. In particular, Volume 2 has been a hoot and a half, as former teenage B-list heroes try to help those who used to be in their situation...such, our less-than-enthused heroes. Cue wacky hijinx. Again, don't worry that you have to be steeped in Marvel lore to enjoy the title, but if you're a recovering Zombie, this is crucial reading.
So, hie thee to Amazon! The first volumes of
Y The Last Man,
Ex Machina, and
Runaways are all available for ten bucks or less. Alternately, camp out at your local comic shop until they remind you that they aren't a library; then, if you like what you're reading, see if your library has any of the trades avaialble. Even if they don't there's always interlibrary loan. If nothing else, plop your ass down at your local megabookstore where they won't care if you read a stack of trades in one sitting.
FnordChan