12 is Better Than 6

4:3

1600x1200
1400x1050
1280x960
1024x768
800x600

16:9

1920x1080
1600x900
1280x720

16:10

1920x1200
1680x1050
1440x900
1280x800

5:4

1280x1024
1152x864

Dual Monitor

Apple

iPad & iPad 2
Non-retina iPad
iPhone 5/5S (& iPod)
iPhone 4/4S/iPod
Older iPhone & iPod

Blackberry

360x480
320x240

Google Android

1080x960
1280x800
540x960
480x854
480x800
320x480

Netbook

1366x768
1024x600
800x480

Playstation

960x544 PS Vita
480x272 PSP

Windows Phone 7/8

480x800