Some users have reported repeated crashes in Safari for iPad, especially after the iOS 3.2.1 update. Users have reported similar issues, albeit not as frequently, with Safari for the iPhone and iPod Touch.
There are a number of potential causes for this issue, but it appears to occur most frequently when very large pages (especially those heavy with images) are loaded.
Fixes
Turn off AutoFill. Some users have been able to resolve this issue by simply turning off AutoFill in Safari. Go to Settings > Safari > AutoFill and turn all options off.
Close unused Safari windows. Close all unused windows in the application by pressing the page switch button in the lower right portion of the screen then clicking the X at the top left of each page.
Reboot (hard reset). Hold down the sleep/wake and home buttons simultaneously for roughly 15-20 seconds, until the screen powers off then an Apple logo appears, which signifies a reboot. Some problems may require (oddly) that this procedure is performed twice.
Reset all settings. The reset may restore disengaged hardware components and clear corrupt data that prevents proper connectivity. Navigate to Settings > General > Reset > Reset All Settings. Note that this will erase stored messages, passwords and other information.