Strength and tempo of directional selection in the wild   (Proceedings of the National Academy of Sciences, USA, Vol. 98, Issue 16, 9157-9160, July 31, 2001) - This article documents 993 measurements of directional selection in the wild.  The authors have provided a database of instances of natural selection in the wild, as reported in Kingsolver et al (2001) The American Naturalist 157(3): 245-261: http://www.bio.unc.edu/faculty/kingsolver/lab/Kingsolveretal.SelnDatabase.norepdur.3.2001.xls . Note that these studies all deal with directional selection, not purifying or stabilizing natural selection, which creationists sometimes falsely claim is the only kind of natural selection that occurs in nature.

John Endler's classic book "Natural Selection in the Wild" (1986, published by Princeton Univ Pr; Call Number: QH375 .E53 1986 ; ISBN: 0691083878 )  can be found in most university libraries and is availiable from Amazon.com.

"Adaptive Genetic Variation in the Wild" (1999, published by Oxford University Press; Call Number: QH401 .A395 2000 ; ISBN: 019512183X) by Timothy A. Mousseau (Editor), Barry Sinervo (Editor), John A. Endler is also recommended.

"Selection in Natural Populations" by Jeffry B. Mitton.(1997, published by Oxford University Press, Call Number: QH371 .M68 1997 ; ISBN: 019506352X)