I'm looking for resources, either print or online, which compile lists of examples of linguistic phenomena, be they phonological, morphological, syntactic, or semantic. (My main purpose for these would be for teaching linguistic principles and theories, and designing exercises.) I suppose the canonical example of such a resource would be the Source Book for Linguistics by William Cowan and Jaromira Rakušan, which tabulates examples from many different languages and dialects. Can anyone point me to any similar books or online resources?
It depends on your linguistic viewpoint.
For typology, a good wealth of examples can be found in WALS online.
Assuming that you want data that would be suitable for problem sets, you could start with Gleason's Workbook in descriptive linguistics, and Ronald Langacker's textbook Fundamentals of linguistic analysis, still available at the original price. There is a textbook Laboratory manual for morphology and syntax in various editions, published by SIL and usually (currently) with William Merrifield as author -- there is or was a version available online from them though I can't tell you where (it may also be in Spanish). Most phonology textbooks have problem sets, though they are usually too difficult for absolute first level classes, or they require the student to have memorised particular ideas of likelihood in order to get the right answer.
Another approach is to look through journal articles in journals that specialize in language areas, such as Studies in African linguistics or Oceanic linguistics. They often publish descriptive articles that lay out some simple phonological problem in Margyi, pronouns and transitivity in Lushootseed, or Kwara'e tense paradigms. Usually you can skim quickly to see if there are any paradigm-rich papers in an issue. Likewise, you can get problems from some grammars, though often grammar just leave you to figure out what the rules are on your own.