I think it is important to tie technology to the objective because it allows students achieve at the level that you expect, but in a way they prefer. I love using centers and small group instruction in my classroom. It is important that students be held accountable for the work in the centers so that you know they are mastering the objectives. They need to submit work a product, evaluation or reflection to ensure the learning is taking place.
One site that I enjoy using is MangaHigh. The students enjoy competing with each other at the various games and I like that I can easily track their progress. It is also helpful having a variety of ability levels to meet the needs of all the students. This could be easily used in stations. The scores are submitted to me, thus creating a high level of accountability.
Another site I found helpful for Algebra and Geometry was Manipula Math. I like this because it has applets over various topics that can help explain the "whys" behind a concept; They are a simple visual that can be used either individually by students or as part of instruction. To use this in stations, I would need to have the students give an explanation in their own words of the concept. This would be a great way for them to take pre-notes for a lesson.
One app that I could use on the iPad or iTouch is Angry Birds for Geometry. This iPad sensation deals with angle trajectory. As a station, the students could report their highest level achieved and their damage points. The competition alone in a Pre-AP class is incredibly motivating. Another app that I plan to use for Geometry when studying transformations is Tetris. This is one of my all-time favorite computer games and applies the concepts of translations and rotations in a fun setting. The students would compete and report their highest number of lines achieved.
Another way I plan to use the iPad is for GoogleSketch. The students can create geometric figures that they use to discover attributes and make conjectures.