The Distimo iPad Report, shows the largest category is games followed by entertainment, and education. Games rule more on the iPad. Apps cost more on the iPad than iPhone/iPod.  Medical apps cost the most.

• In total, there are 2,385 applications that are available exclusively for the iPad. The largest category on the iPad is Games with 833 titles (35%), followed by Entertainment and Education with 260 and 205 titles, respectively.
• Games and Entertainment applications are more popular on the iPhone than on the iPad: 70% of the most popular applications on the iPhone are published in either one of those categories, compared to 40% on the iPad.
• 83% of applications on the iPad are paid, while only 73% of all applications are paid on the iPhone. The average price of all paid applications that are solely compatible with iPad is $3.61 compared to $3.55 for applications compatible with iPhone.
• Medical applications are most expensive on both the iPad ($9.39) and iPhone ($10.73). On the contrary, Education ($9.10), Healthcare & Fitness ($4.41), Music ($6.86) and Sports ($4.95) applications are significantly more expensive on the iPad. Books are currently cheaper on the iPad than on the iPhone which may be influenced by the iBookstore availability on the iPad.

You can download the report for free here.