I've loved Universalis for a while now (we've linked it from the left sidebar on the front page) becaause it takes the flipping and figuring out of praying the Liturgy of the Hours. The right antiphons and readings come up in linear fashion based on the date and time on your computer. I've always thought that the first app I'd get if I got an iPhone would be Universalis' mobile version.
Another parishioner swears by DivineOffice.org. Their version of the Liturgy of the Hours is audio, complete with music. I can verify that the production values are very nice and the recordings are beautiful. They also have a mobile version. It reminded me of the podcasts on Pray As You Go, only with the prayers of the Universal Church. There are lots of great Catholic prayer aids out there to accompany your digital, plugged-in lives. If you have some you want to share let us know and we'll blog them too.