There's a lawsuit pending by the estate of the late Randy California (of Spirit *), stating the first 1/3 of "Stairway to Heaven" was stolen from his song "Taurus". Here's a short article with what's going on, a sort-of rebuttal by Mr. Page and a comparison game to see if all this has merit. Included in the article is a table showing previous lawsuits, most going against Mr. Page. Also there's this NYTimes interview, with Mr. Page further rebutting allegations AND pimpin' the merch: Newly-remastered versions of all their recorded material with high-zoot vinyl available. Expensivo, and part of the reason for the lawsuit now--to get proper credit included.
A respected estimate in '08 put "Stairway..." earnings at $562 Million.
* Spirit was a short-lived band with original songs and excellent playing. Look for them in "Unheralded...", with Crack the Sky, soon.