I use seatguru.com often but can never remember the site that is similar and what about airlines not covered by them? This link is to a site that links to seatguru or seatexpert and for those not covered it links to the own airlines web sites. Pretty good IMHO. Not sure how extensive or up to date all links are, but found it through google and thought I'd share

http://www.airtimetable.com/seatmaps.htm