My favorite high visibility font is Tiresias and it even shrugs off the effects of the error dispersion being applied to PDF documents by the Sony Reader. Most PDF generators can embed it into your PDF documents. It will not be available in RTF unless you do the re-flash procedure to add it as an available system font. It is available as a True Type font so it can be embedded in BBeB documents.
http://www.tiresias.org/fonts/index.htm