The market is assumed to have perfect information to the price is assumed to reflect all publicly available information. As such, credit ratings or bond yields provide insight into how the market views this company, based on all publicly available information. There is no guarantee that any source is going to have the information you seek. Indeed, once could waste a lot of time, especially if one is determined to hunt down unique sources of information for each competency and capability. Most of this information can be found from the top 2-3 sources; other sources may not be entirely superfluous but the researcher must understand that there is a point of diminishing returns with respect to most sources in the library or Internet. A search of an academic database can take hours to yield two useful articles, neither of which sheds any more light than what can be found on the first page of a Google search. It is important that the researcher is able to prioritize sources -- the quality of the references is more important than the number of references, assuming the objective is to learn something.

Most sources listed offer at least the potential of usefulness in an internal analysis. Company sources may be the most forthcoming with respect to resources and competencies, but they are also the most biased. Trade magazines, newspaper articles, analyst reports and academic journals are far more objective in nature, which can lend balance to the analysis. Inference is also critical. The financial statements, for...

Remember that annual reports must contain a substantial amount of information by law -- enough information for investors to make a rational decision about the company.
Resources:

2009 Annual Report: Retrieved May 15, 2010 from http://phx.corporate-ir.net/External.File?item=UGFyZW50SUQ9NDA3OTd8Q2hpbGRJRD0tMXxUeXBlPTM=&t=1

Q1 2010 Financial Results Conference Call Transcript. Retrieved May 15, 2010 from http://phx.corporate-ir.net/External.File?item=UGFyZW50SUQ9MjU2NDQ5NXxDaGlsZElEPTM3ODMzNHxUeXBlPTI=&t=1

Dallas Morning News. (2010) SouthWest, WestJet cancel code-sharing agreement. Dallas Morning News. Retrieved May 15, 2010 from http://www.tradingmarkets.com/news/stock-alert/dalw_luv_wjavf_southwest-airlines-westjet-cancel-code-sharing-agreement-918553.html

Brown, T. (2009). Corporate innovation at Southwest Airlines: An interview with Herb Kelleher, founder and former chair & CEO. Business Horizons. Vol. 52 (5) 409-412.

Weiss, D. & Maher, M. (2009). Operational hedging against adverse circumstances. Journal of Operations Management. Vol. 27 (5) 362-373.

ATW. (2009). Southwest reaches tentative deal with pilots, adds three routes at DEN. Air Transport World (Online edition). Retrieved May 15, 2010 from http://atwonline.com/airports-routes/news/southwest-reaches-tentative-deal-pilots-adds-three-routes-den-0309