In some textbooks they don't talk about "rules" so much as "patterns." At least knowing that there's a limit might be helpful to some learners.
Here's one version:http://books.google.de/books?id=brxvMZ8VgP8C...
(p.104 or search for "noun plurals")
Here's a table with more examples:http://nthuleen.com/teach/grammar/pluralexpl.html
I can think of a few "rules" (of course there's exceptions) that I have learned over the years, though:
-Foreign nouns often take -s: Hotels, Taxis
-many masculine and neuter nouns ending in -er and -el don't change in plural: Lehrer, Kabel
-feminine nouns usually take an -n or -en: Türen, Gabeln (For Gabel, I always have to remember the 2nd rule, that it's just the m and n nouns that don't change.)