Just go to flightlookup.com. It redirects to eskyguide.com (an AmEx site); flightlookup.com should be easier to remember (for times when you don't have a bookmark handy). The search results, very conveniently for WN fliers, are sorted by number of connections. So a WN direct flight will be listed right at the top of the page if nobody flies the route non-stop. A good example search pulled from another topic: STL-SMF. On 02-Jan-09 WN735 stops at LAS; on 30-May-09 WN1421 stops at PHX; on 26-Jun-09 WN1239 stops at PHX; on 11-Nov-2009 WN1239 stops at PHX; on 20-Feb-2010 WN1421 stops at PHX.

Oops! Apparently you have to know not to put in dates beyond WN's booking window.

Also, the site doesn't know how to increment the stops counter. It says that on 20-Feb-2009 WN1874 has "1 stop via DEN-SNA." Southwest does list that flight as having two stops. I have not used the pdf technique to verify any of these results.

You can click on the flight number to see details such as scheduled departure and arrival for each segment and the equipment type.

One final caveat/useful bonus: on one route I looked at the search results included a custom connection that is not WN published, scheduled service. That custom connection information can be useful when award seats are hard to find. There is no guarantee the custom connection will be one that qualifies for single coupon booking (and in this case it was not), but it can be good information.