There are android apps for the Borders, Barnes and Nobel's, and Amazon's book readers. Anything you can read on those stand alone devices you can read on android. A stand alone reader would be easier to read in the sun but if most of your reading will be inside a phone or tablet device would work fine. As mentioned above Aldiko is another reader. It is also the one I use.
Calibre is open source software that will convert various e-book formats from one to reader format to another too. This includes PDFs.
calibre - E-book management
Input formats CBZ, CBR, CBC, EPUB, FB2, HTML, LIT, MOBI, ODT, PDF, PRC, PDB, PML, RB, RTF, TXT
Output formats EPUB, FB2, OEB, LIT, LRF, MOBI, PDB, PML, RB, PDF, TXT