The free agent market for catchers is uninspiring. When the marque name is a 36 year old Ramon Hernandez, you know the pickings are slim. He's likely to command a multi-year deal in the neighborhood of $4M per, so no thanks. There are other viable options like Ryan Doumit, Chris Snyder, Rod Barajas, Ramon Castro, and Jose Molina, but I'd rather not guarantee any of them millions just to catch roughly 40 games.
Carlos Ruiz is the starter. When healthy he's on the field at least 5 times a week. Most of the catchers listed above want more playing time than what they'll likely get in Philly. Therefore, I suggest going cheap. Not Brian Schneider cheap either. Schneider is old (35) and can no longer hit or play solid defense anymore (-0.9 WAR in '11).
1st Choice- Erik Kratz. He's already in the Phillies system and has proven that his bat is worthy in the minors (.267/.810 in AAA), and he's gunned down 33% of base stealers too in 10 minor league seasons. He's a 31 year old "hometown" boy from Landsdale and is familiar with some of the Phillies pitchers because of spending last year in the organization.
2nd Choice- Max Ramirez. At one time, this 27 year old was a big time prospect. He's since been bounced around from organization to organization and lost that label. His minor league stats are encouraging- .295/.867 and even in 45 MLB games has shown the ability to get on base (.343 OBP) despite a low batting average (.217). He's the perfect guy to sign to a minor league contract and have compete for the backup job in spring training and stow away in Triple-A if he doesn't seize the opportunity to start the year.
3rd Choice- Ivan Rodriguez. Amaro has already added one ancient future Hall-of-Famer (Thome) to the 2012 Phils, why not another? Pudge remains an excellent defender and his desire to continue catching remains high in his quest for 3000 hits (currently at 2844). Sell him on the chance to handle the Phillies pitching staff and the shot at a World Series title and it might not take much to lure him to Philadelphia.
Other Options- Wilkin Castillo, Robby Hammock, Corky Miller, Omir Santos, Jose Morales, and Brad Davis all have MLB experience and are minor league free agents, so they will come cheap and add depth in the minors if not awarded the backup job out of spring training.