Mail Readers that Don't Display Exterior Graphics
Luckily, there are several email programs that interpret the innocuous parts of HTML (bold and italics, for example) without displaying Web Bugs and other exterior graphics:
Eudora 5.1 for Windows and Mac OS: http://www.eudora.com/.
Evolution for UNIX/Linux: http://www.ximian.com/.
Mail.app for MacOS X: http://www.apple.com/macosx/.
Entourage, part of Office 2001 for MacOS 9 or Office X for MacOS X: http://www.microsoft.com/macoffice/.