I know about NLS, and some of the mitochondrial, but is there any good (and recent) review covering those sequences and the proposed mechanisms for their action?
This page shows a scoring system used for predicting how well proteins with sequences target to certain regions/organelles. Not the easiest to understand, but a good place to start before checking the lit on their suggested motifs
restricted to NLS (as an example of a sorting peptide) you may try the following:
Lange A, Mills RE, Lange CJ, Stewart M, Devine SE, Corbett AH.Classical nuclear localization signals: definition, function, and interaction with importin alpha. J Biol Chem. 2007 Feb 23;282(8):5101-5
Xu D, Farmer A, Chook YM.Recognition of nuclear targeting signals by Karyopherin-β proteins. Curr Opin Struct Biol. 2010 Dec;20(6):782-90
For prediction, along with WoLF PSORT, I would also recommend Eukaryotic Linear Motif: http://elm.eu.org