Viewport sizes for iPad, iPhone 4 and under, and iPhone 5 and up.

gistfile1.txt

iPad (Actual pixels in brackets)

1024 × 690  (2048 x 1380) In landscape on iOS 4.3
1024 × 672  (2048 x 1344) In landscape on iOS 5
768  × 946  (1536 x 1892) In portrait on iOS 4.3 
768  × 928  (1536 x 1856) In portrait on iOS 5
             
1024 × 660  (2048 x 1320) Always showing bookmarks bar in landscape on iOS 4.3
1024 × 644  (2048 x 1288) Always showing bookmarks bar in landscape on iOS 5
768  × 916  (1536 x 1832) Always showing bookmarks bar in portrait on iOS 4.3 
768  × 900  (1536 x 1800) Always showing bookmarks bar in portrait on iOS 5
             
1024 × 748  (2048 x 1496) In full-screen mode in landscape
768  × 1004 (1536 x 2008) In full-screen mode in portrait
             
1024 × 768  (2048 x 1536) In full-screen mode with translucent status bar in landscape
768  × 1024 (1536 x 2048) In full-screen mode with translucent status bar in portrait

iPhone 4s and lower (Actual pixels in brackets)

480  × 208  (960  x  416) In landscape
320  × 356  (640  x  712) In portrait
320  × 336  (640  x  672) With in-call status bar in portrait¹
             
480  × 268  (960  x  512) With address bar hidden in landscape
320  × 416  (640  x  832) With address bar hidden in portrait
320  × 396  (640  x  792) With address bar hidden with in-call status bar in portrait
             
480  × 300  (960  x  600) In full-screen mode in landscape
320  × 460  (640  x  920) In full-screen mode in portrait
320  × 440  (640  x  880) In full-screen mode with in-call status bar in portrait¹
             
480  × 320  (960  x  640) In full-screen mode with translucent status bar in landscape
320  × 480  (640  x  960) In full-screen mode with translucent status bar in portrait
320  × 440  (320  x  880) In full-screen mode with in-call status bar in portrait²

iPhone 5 (Actual pixels in brackets)

568  × 208  (1136 x  416) In landscape
320  × 444  (640  x  888) In portrait
320  × 424  (640  x  848) With in-call status bar in portrait¹
             
568  × 268  (1136 x  536) With address bar hidden in landscape
320  × 504  (640  x 1008) With address bar hidden in portrait
320  × 484  (640  x  968) With address bar hidden with in-call status bar in portrait
             
568  × 300  (1136 x  600) In full-screen mode in landscape
             
568  × 320  (1136 x  640) In full-screen mode with translucent status bar in landscape

¹ The height of the status bar doubles in-call, but only in portrait orientation.
² The In-Call Status Bar turns opaque, but only in portrait orientation.