I'll just list people who are still in good shape. Guys like Sabu are broken down and Sean O'Haire missed his spot and isn't looking wonderful these days either and Matt Bentley joined a band so they don't really count.
Rob Van Dam - Obvious chance but heck the dude is uber talented and he would be great back in WWE on say the Smackdown brand, some great guys to work with, he would also fit in well with TNA, heck I know most want to see him compete against the likes of AJ Styles and Samoa Joe.
Mr. Kennedy - Is another big one and I'm guessing he won't be for long, once his 90 days expires most expect him to appear in TNA.
James Mitchell - He is one of the best free agent "Managers" in the wrestling business, the fact that neither of the big two have him is criminal, he could get some many people over who badly need a mouthpiece.