Who's looking for one: Angels, and Tigers
Who's available: Chris Iannetta, or a trade
The Angels have lost Chris Iannetta to free agency and now they only have Carlos Perez so they most definitely need to get someone. I think that the most likely option is simply resigning Chris Ianetta. However Ianetta and his agent are certainly aware of this and now that Matt Wieters is off the market will probably be trying to get a huge contract. The tigers still have James McCann who caught most of last season, but he is one reason why the Tigers had a very disappointing 2015 season, and I believe they will go after someone on the trade market to make a difference. For example if they traded for Jonathan Lucroy it would earn them almost 3 more wins. However the Tigers do not have a lot of options for trade, so it's also possible they will just resign Alex Avila.
Second Tier Catchers:
Who's looking for one: White Sox, Rockies,Yankees, Blue Jays, and Marlins
Who's available: Alex Avila, Dioner Navarro, Geovany Soto, Jarrod Saltalamacchia, Brayan Pena, or a trade
These teams have players who are ready to start every day but have no real back up, and aren't invincible like Salvador Perez. These free agents would be earning somewhere from $2-7 million/year over 1-3 years. I also think it is possible that one of these teams will trade for a player as they have strong farm systems to deal from.