Welker may start the year on PUP (6 weeks) but I have a good feeling about his availability and health. Obviously we need players though, since Aiken/Stanbeck won't get it done and Tate is an unknown.
Breaking down the free-agent class of an unpredictable offseason
is a old but comprehensive list of all UFAs in an uncapped year, assuming no re-signings which obviously won't happen. It's pretty dire.
WR: Arnaz Battle, Marty Booker, Antonio Bryant, Nate Burleson, Tim Carter, Chris Chambers, Antonio Chatman, Terrance Copper, Bobby Engram, Brian Finneran, Mike Furrey, Greg Lewis, Brandon Lloyd, Derrick Mason, Shaun McDonald, Sean Morey, Muhsin Muhammad, Kassim Osgood, Terrell Owens, Josh Reed, David Tyree, Bobby Wade, Kevin Walter, Kelley Washington, Ernest Wilford.
Out of those: Bryant, Burleson, Muhammed and Owens are the ones that I know as credible starters. Derrick Mason is a great player but may retire and has huge health issues. I've heard of Osgood positively but nothing more.
More likely is picking up a player who will be cut, e.g. Deion Branch or maybe even Donte Stallworth.
Alternatively look to the draft and try to find a 5th round WR who can catch the ball in traffic and run his routes precisely. Give him simple non-option routes and see what he can do with them, and then slowly build up his playbook.
In the top rounds I like Arrelious Benn as the next Boldin, but he's probably gone by the end of the 2nd round and we have other needs and opportunities to pick up WRs.