Are there any good alternatives to the Explorer web browser? I would really like to be able to view web pages when my PDA is turned 90 degrees.

(Palm has an inbuilt function that can tilt the window 90 degrees)

Bitstream Thunderhawk is a great alternative that you may want to look at then. It is not so much a browser as a proxy service with a browser, but it definitely turns everything landscape.

http://www.bitstream.com/