We got our iPad after the seder last year. So this is the first year we can explore the Passover apps. We confine this brief list to free apps plus one at .99. There are others at reasonable prices. Here they are:
No Chametz! - free - what you need to search for Chametz and a link for selling it for a fee.
iSellChametz -free - Rabbi Shmuel Herzfeld of Ohev Sholom - the National Synagogue - will sell you Chametz at no charge. Donations to his synagogue suggested. Find this app on the Android Market called "Sell My Chametz".
OU Passover - free - magazineware of the OU guide for Passover certified kosher foods.
Fishing - free game - not sure what it has to do with Passover - but will keep a 4 year old kid occupied for a while
PlagueAudio - free - cute sound effects for the ten plagues
iHagada .99 - Not (yet) for use by observant Jews at the seder. Has the Hebrew and English texts for the Seder. Or try other Haggadah Android apps.
Just open iTunes or Android Market and search for "Passover" to find those and more.