My 2-cents (actual value may vary)...
Given those options, I'd support the Zed wholeheartedly.
Although the S2000 is an admirable performer, it's feeling a bit "long in the tooth" to me. And with the possible exception of the original Miata, the finest examples of roadster designs emanate from Europe. The "flame" styling of the Zed isn't for everyone, but it makes a uniquely distinct and sculptural statement. I also prefer a classic analog driving interface, and the S2000's video game dash isn't for me (but tastes vary). Lastly, the Z feels practically cavernous compared to the Honda's cramped quarters.
The Boxster is a more than capable road-hugger, but it seems almost too precise — almost to the point that it's less "seat of your pants" fun. Depending on the year, the button-festooned cockpit is nothing special and makes you feel the same. Even though more recent years have improved on interior finishes, it still feels less sporting. And although the Boxster is a case study in design evolution, it is a dime-a-dozen on the roadways (if you're looking for a bit of comparative exclusivity).
FWIW, I was recently in similar shoes... cross shopping the new TT and a beaut of a 2007 Cayman, when the local BMW dealer unexpectedly got an even more beautiful 2007 3.0Si Coupe. I previously had two roadsters (Z3 and TT) so was looking for coupes. The Z4 Coupe's style was so striking that it never even made it to the lot... The TT and Cayman are great cars, but the Z4 makes you feel special. Everything from the seating position, to the spartan "road-focused" interior to the pounding rumble of the horses out front just comes together.
You have the benefit of considering some great cars, though. And you're certain to opt for the best for you. But for the money, it's hard to beat a Z.
Cheers!
