Screen Resolutions
iPhone 3, 3G
320x480px
iPhone 4, 4S
640x960px
iPhone 5, 5C, 5S
640 x 1136
iPhone 6
750 x 1334
iPhone 6 Plus
1242 x 2208 (seen by apps) which is downsampled to an actual screen output resolution of 1080 x 1920 (explanations here and here)
iPad1, iPad2, iPad Mini original
768x1024px (20 pixels taken up by top bar)
iPad 3rd Gen, iPad Air, iPad Mini Retina
1536x2048px
Good Screen And Element Size Resources