I've become very addicted to my iPhone lately. Countless hours in the dark spent trying to put a baby to sleep were much more interesting when I could check email and look at facebook. And now I can blog from my phone, too! Hurray!
I'm disapointed that there doesn't seem to be a good plant ID guide. Maybe someday! Right now here's a couple apps for gardeners:
You can search by ingredient, including that veggie you grew too much of.
More detailed hourly reports help you figure out when to water and when to let nature do the watering.
I've spent way too much money on plant books since I started having a mobile wishlist.
What I'm using now!