Here are some good open source Android apps I've installed from the F-Droid app store.

K-9 Mail: Simple setup, works with IMAP, POP3 and Exchange 2003/2007 (with WebDAV) accounts.
RedReader: A really good Reddit client
AntennaPod: In the absence of Gpodder thus far, I've found a podcast client that searches the gpodder.net directory and accepts opml imports of your existing subscriptions.