+1 for Goodreader. Such a usable app. You'd think a pdf reader is a pdf reader, but there are many small features and UI niceties I would miss if I switched from Goodreader. I wish there were something as good for Android.
On Android (and jailbroken Kindles) Koreader (open source on github) does a decent job of reflowing even 2-column PDFs.
On Android (and jailbroken Kindles) Koreader (open source on github) does a decent job of reflowing even 2-column PDFs.