Gowerpoint's µBook (http://www.gowerpoint.com/uBook_main.html) deserves much recognition for being one of the most complete e-book reader solutions available for Pocket PCs. Not only can it read a whole bunch of file formats (including HTML, TXT, RTF, and PDB) but it also offers a wide range of customization options including portrait and landscape display, choice of font type, color and size, and a completely skinnable UI. Version 0.9g adds support for embedded PNG in RTF files and includes various bug fixes.

You can download the trial from here (http://www.gowerpoint.com/uBook_down_nf.html).

Thanks to eyoung for the tip!