Prince of Persia beat Sex and the City 2, but Shrek Forever After stayed at the top of the box office for the Memorial Day weekend.  Iron Man 2 came in fourth with Robin Hood rounding out the top five.

Results: 

1. Shrek Forever After
$55,700,000

2. Prince of Persia: The Sands of Time
$37,800,000

3. Sex and the City 2
$37,100,000

4. Iron Man 2
$20,600,000

5. Robin Hood
$13,600,000

6. Letters to Juliet
$7,300,000

7. Just Wright
$2,700,000

8. Date Night
$2,300,000

9. MacGruber
$1,900,000

10. How to Train Your Dragon
$1,500,000

(Source)