I've not yet found a single application that represents a full GTD-solution for me. One of the parts that I really like in my current GTD-suite is netMemo (for "dumping" my brain into the inbox & general idea and thought capture while on-the-go). It let's me record a voice note with only two clicks, and then delivers the recording to my regular e-mail inbox as an mp3-attachment, where I can't miss it.
http://play.google.com/store/apps/de...netify.netmemo