Try Aldiko for EPUB, it can even handle DRM

, and ezPDF for PDF files, but that is not for free, but works great. It has a working annotation feature and allows for free panning in every zoom level

.
Another one for EPUB is Moonreader+, but I don't like it

, and there is also a fbreader available, but I haven't tried that.
For these apps you'll need to install
Android market, if not already done, and
Apps2SD may be helpful, but for that you'll have to start from scratch, because it possibly will destroy the data on your SD card