I would agree with you whole heartedly if the OP wasn't looking for something for this summer. Phuket will be HOT not warm. I was just there last month and it was nice and warm. I asked the hotel staff what it was like in the summer and they said it was hot, even at night - 100 F.

The Caribbean destinations are great because it is actually cooler (that's a relative term) than some places in the US thanks to the cool breeze from the water. Also many places in the Caribbean run specials during the summer.

Ritz Carlton in Grand Cayman is suppose to be very nice; I would not recommend the Marriott there.

Curacao I like, and is especially nice if you dive.

If you like the large resorts and touristy spots then the Cancun and Aruba properties woudl be good choices.

Hawaii is nice, but definitely not low season; although their tourist economy has been hurting so perhaps there are some deals to be had. The nicest islands are Kauai and Maui, and the nicest hotel is the JW Marriott Ihilani on Oahu.