Repositioning cruises are usually in the printed brochures but are harder to find on the lines' web sites. You almost have to look ship by ship (i.e. here are the Alaska cruises, here are the Mexican Riv cruises - the repo must be in between).
A Bad Day At Sea [with power] Always Beats A Good Day At Work
Alaska 2014 - haven't picked a cruise yet
Carnival: Glory 2004, Destiny 2008, Splendor 2009, Freedom 2011, Valor 2012
Celebrity: Summit 2011
Princess: Ruby 2010, Caribbean 2013