I just came across a resource and a name that are both cool enough to be worth adding a comment here.
The resource is the Real Names of Famous Folk site, which lists lots and lots of pseudonyms of all varieties.
The name is (are you ready for this?): Ramon Felipe San Juan Mario Silvio Enrico Smith Heathcourt-Brace Sierra y Alvares y de los Verdes, which was apparently Lester del Rey's original name. At least, according to that site; there are other sites that disagree (generally adding a "-del Rey" after the "Alvares"), and I corrected "Uerdes" to "Verdes" on scant evidence. So that may not be precisely accurate. But it's somewhere in the neighborhood, anyway, and pretty cool.
(Last updated: 6 June 2002)