From: Montreal, Canada
I currently own 4 books on Greece/Crete. I haven't had the time to really dwell much into them yet, though.
1) Greece and Crete 1941, by Christopher Buckley. Only read a few chapters, but it was been an interesting read. Short-ish, global overview of the war on Greece/Crete against the Germans from the British perspective (not much on the Italians). Picked it up based on the recommendation of one of the Conquest of the Aegean research guys.
2) Crete: the Battle and the Resistance, by Anthony Beevor. Apparently the best book on Crete. I've never read Beevor before, so don't know what to expect.
3) Air War for Yugoslavia, Greece and Crete 1940-1941, by Christopher Shores. Apparently covers the entire air campaign for Yugoslave/Greece/Crete in good detail. You could probably only find this used. I had to pay a nifty amount to import it new from Japan, of all places.
4) An Abridged History of the Greek-Italian and Greek-German War 1940-1941. This is the official publication of the Army History Directorate of the Hellenic Army General Staff. English abridged version of a series of 7 books (which is in Greek only). I haven't read it yet, but this seems like the DEFINITIVE version if you're interested in the Greek side of things, because there are lots (not sure on the exact number from memory) of large, detailed fold-out maps throughout the book, which really impressed me. This book can mostly only be found used, and even then can be found sold for over 100$ (youch!). If you're keen on getting it, though, this is the one place I've managed to find it at that doesn't try to completely rip you out (they import it from Greece), 40$ new http://caratzas.com/index.cfm?fuseaction=product.display&product_ID=359
Hollow Legions by Mario Cervi is one book that focuses mainly on the Greek-Italian war from the Italian perspective, but I can't find it new and don't even know if it's actually good (can't even find any reviews).