I give my clients the most common is in regards to insulation around the perimeter rim joist in the basement or crawlspace. Historically, the most popular method of adding insulation has been to stuff fiberglass insulation into these spaces. I have recently purchased and used what I believe to be a far superior method for sealing this common air infiltration area.
foam from Guardian Energy Technologies called Foam-It-Green. Foam-It-Green is an easy to use product that is delivered as a ready to use 2 part system with easy to understand directions and all of the spray attachments needed to do a professional job. The biggest benefit in using foam to seal the rim joist or even larger areas is that it seals drafts AND offers a good R-Value. Fiberglass insulation alone is a poor choice for sealing drafts.
YouTube video here! http://www.youtube.com/watch?feature=player_embedded&v=f_xHejjopkI#!
The people at Guardian Energy Technologies are very friendly and responsive to questions. I encourage you to visit their website: http://www.sprayfoamdirect.com/home-owners/residential-applicationsand get more information on this and other products that they sell.