This is an excellent site which allows you to search by topic, Bloom's Taxonomy, grade level, price, subject, and even type of mobile device to locate relevant apps.
This teacher blog categorizes apps for the iPad by subject area in the elementary school.
SIG 1 context: mobile devices, iPad and apps for exploration/ creation
***Rachel you might want to view her listing of apps for creation****
This is a short review of iPad apps for elementary students focusing on math, science and reading. This is further broken down by grade level from a teacher "in the trenches." This is valuable because it is a practical overview for easy decision making and location of apps for the elementary. All apps listed here are not free
SIG 1Context: mobile devices, iPad, elementary
Designed by math teacher Thomas Petra to share meaningful, practical math lessons with other teachers. Lesson ideas, examples, downloads ....the goal in each case is 21st century learning that uses Google Earth to help make math real and relevant to students.
Examples include finding the volume of the Great Pyramids of Giza, converting currency, working with time zones, noting the locations of a storm to map its progress over time....