How can I archive articles I'm reading on my iPad? (Evernote, Instapaper, etc)
I find the Send to Instapaper button to be perfect for archiving because it's so ubiquitous. The glue that gets your articles from there to Evernote is IFTTT.

Just create a rule that says anything you save to Instapaper gets imported to Evernote and you're set. I believe you can automatically have it add a tag at the same time.