Most of these will work with iPad or Android tablets.
Magic Plan app from Sensopia for the iPad/iPhone/Android exports and integrates the drawing with 20-20 Design Version 10. You create your account under File, Preferences, Magic Plan link. You login to that account in Magic Plan. Create your layout and choose Export in Magic Plan. Pick the 20-20 Design option and it sends the drawing to your 20-20 Design computer. Open the drawing and start selling your job! Senopia does charge for the Export.
See Sensopia information here: http://www.sensopia.com/english/index.html .
See MagicPlan in action here: http://www.youtube.com/watch?v=DMv82x96oK8
My Measures Pro - take job site photos and annotate
Quickoffice - open and edit Microsoft Office files
Evernote - shares notes between all your devices
Dropbox - share files between all of your devices (see my blog on this)
My Sketch - take a jpg and do many type of charcoal sketches
Tom Bachorski, 20-20 Authorized Industry Consultant