I just got back a few months ago from an extended trip, with my iPod Touch, to South America. The iTouch is great for travel because you don’t need a plan for WiFi, and it does Skype just fine.
Though there were a few choices, I finally settled on paying $9.99 for Wiki Offline by Avocado Hills . This was by far the best app for the trip. I loved reading background and history, even for a surprising number of medium-sized places.
In contrast, Word Lens by Quest Visual proved to be a complete waste of money.
I found another unlikely app to be most handy, the free MapsWithMe – Travel Guide by Yury Melnichek . This is great for two reasons. It had all the free offline local maps I needed for the whole trip, and contained all the offline Wikitravel I needed.
I really love the Web Reader – Text to Speech $1.99 app by Chris Chauvin ; because, I filled my Mendeley – Reference Manager app  with 1,000 research PDFs and listened to them to my hearts content. ;^)
Finally, I ended up buying the Justin.tv app  for $4.99 en route, just to get some free English language TV. Despite containing atrocious advertising for a paid app, it really surprised me what all you can watch on Justin.tv. ;^)
I never did locate a really good *offline* podcast app.