Calibre would work, but you could also send the text to something like Evernote, which supports tagging, highlighting, text formatting, easy searching, etc. It will sync with all of your devices and is searchable. With the browser plug-in, you can choose to save the whole page or just the text / blog post you're interested in keeping. One caveat: it's possible that only the premium service allows for offline storage on your iOS devices -- not sure.