Easily the best free agent pickup was either:
1. Jim Hart, an undrafted free agent QB out of the SIU-Carbondale Salukis. He played 18 years for the Cardinals with a record of 201-136 with 34,000+ passing yards.
2. Don "Air" Coryell. Somehow, Billy Bowtie let someone pry open his wallet and hire the guy who was already known for developing the "I" formation as a college coach. Coryell inherited a shitteh team in the ashes of skinflint Walter Wolfner and that probate battle. He turned them around in one season. Unfortunately, Billy Bowtie's wallet sprang back to form like a bear trap, and Coryell was fired. Moving to San Diego, he only invented the modern passing offense, hiring guys like Jim Mora (insert chuckle here) and Joe Gibbs. But his first years as a pro jock were with Los Cardinales.
...and if you've never seen a Saluki, google it. Beautiful.