I usually take pictures of my readings, too. If I really want to remember what one was about, then I add the reading and/or photo to Diaro (it's a mobile journal app that syncs to the web). You can add pictures, tag entries, use the web version to print nice PDFs, and it has a clean and attractive user interface. Most importantly (for me), it can be password protected.
If I'm doing electronic readings, such as with Fool's Dog apps or Galaxy Tone apps, it's easy to save them right within the app themselves with hardly any effort.
Someone mentioned Evernote, which I agree is great for information gathering and organizing, but I don't use it for anything sensitive like personal readings or journal entries. You can't password protect individual notebooks, which is why I've chosen Diaro for stuff I want to keep away from prying eyes. In addition, I have so many Evernote notebooks that my database is kind of large and slow, so it's nice to have my journal elsewhere.