i highly reccommend the Z600. it's tri-band, bluetooth equipped, and has tons of features, and it's also very mac friendly. moreover, SE's interface is very friendly and intuitive, the best among cellphones, i'd say. the RF is very good, and ther screen is just awesome. the best in any SE phone so far, and also among other high end phones. if you have the dough, go for the P900.
in the states, there are not many places where you can just walk in and play with the cooler and worthwhile phones. unless maybe if there happens to be a Howardforums meet in your area, then you can go and meet some cool people and try out tons of the best and most cutting edge phones.
in the states, reliable stores would be GSMPhoneSource, Just Talk and a couple others. i'd say any dealer listed in the Marketplace section of howardforums are pretty good places to get phones. they're usually a bargain compared to any outside retailer. and the BST usually ahve awesome deals.