www.CostaRicaTicas.com

Here's a take on what's out there. I expect y'all will report on your unmentioned faves:
http://travel.nytimes.com/2010/02/21/travel/21Prac.html

Extracted from the piece:
meta-search sites:
http://www.kayak.com
http://www.fly.com
http://www.momondo.com
international consolidators:
http://www.vayama.com
http://www.airfare.com
Unmentioned in the article but always a fave:
http://www.farecompare.com

These are all more valuable on air routes that have competition--gonna be more price volatility e.g. the market-busting Southwest did in opening a Philly-Boston route.

_________________
"A man accustomed to hear only the echo of his own sentiments, soon bars all the common avenues of delight, and has no part in the general gratification of mankind"--Dr. Johnson
"Amen, brother"-ED