Ancestry The most obvious app because it's from the most well known site, this app allows you to add to your ancestry.com family tree as you work. Since much work may be done in libraries or on the go having this information on your phone is likely to be very helpful.

GedView Pretty much the same thing as Ancestry.com but not attached to that website or any website. Everything is stored on your phone which could be good or bad, depending on your style.

MobileTree Again, similar to the ancestry.com app but this one is connected to the familysearch.org website. Not sure which one is better but this app does allow you to upload photos, videos and a whole lot more so it's likely worth checking out if you're not already committed to another ancestry site.

Genealogy - Uncovering Your Ancestry Just an ebook to help you get started learning about your ancestry. Not likely the best resource out there but for $1 not a major expense either.