Even within the tiers, I have ranked these in the order I think it's likely they will change teams, from "least likely" to "most likely."
NOT HAPPENING:
Kevin Garnett, Lakers - Just coming into his own as a superstar, there is no way the Lakers aren't going to match him. A super-max wouldn't surprise me.
Michael Finley, Raptors - Anyone who thinks Soundwave is going to let a budding superstar walk away is deluding themselves. A super-max wouldn't surprise me here, either.
Antonio McDyess, Hawks - The Hawks have been built around the premise that McDyess is their offensive focal point; they're not letting a guy who scored 22.2 ppg last season walk away even if they have to pay the luxury tax for the first time.
Theo Ratliff, Jazz - The Jazz have buckets of cap space and Theo allows them to put a defensive-minded big next to Duncan that doesn't care if Duncan gets all the shots. There aren't any other young good UFA centers out there, so no reason to think the Jazz aren't ready to match any offer, even a max offer.
POSSIBLE BUT UNLIKELY:
Jerry Stackhouse, Magic - The Magic may be burning their team to the ground, but I don't think they let Stack walk for nothing - they'd sooner match and trade him away next season than take a bad deal now. Almost "not happening" but this one falls into this category because the Magic are burning their team to the ground and the team that wins the bidding war may find a willing sign & trade partner if they give up young, cheap assets like players on rookie deals and/or picks. One of four players I really think will be interesting to watch, but only because the way he is handled will go a long way to determining what the short- and long-term future in Orlando looks like.
Damon Stoudamire, Spurs - Stoudamire has been more consistent than Sheed, but I don't think the Spurs can afford to pay both. If push comes to shove, I think they keep Stoudamire, though a nice S&T package might sway them. Not very likely to happen, but possible.
POSSIBLE:
Rasheed Wallace, Spurs - Sheed has really declined the past two seasons, dropping from 17 to 13 to just 9 ppg. The Spurs have plenty of cap space to match offers, but know they have to pay Allen and Abdur-Rahim next season. A rich enough offer just might be enough, especially if Stoudamire gets signed. Another guy I think will be interesting to watch because he's got the potential but hasn't lived up to it, and I'm not sure whether back-to-back years of significant decline scares the league off even a young guy like Sheed.
Eric Snow, Hawks - He's been awful offensively but good defensively in four seasons with the defense-loving Hawks, who have publicly said they'd love to keep Snow... if the price is right. Depending on how you look at the drafting of Andre Miller, the Hawks are either ready to move on without Snow (making him easier to get) or have a lot of leverage in any negotiation, since they can't be hardballed with the threat of him leaving (making him harder to get). A guy I think will be interesting to watch in RFA as it will show how much the league values a defensive player who's an offensive liability.
Arvydas Sabonis, Bulls - The Bulls don't want to lose him. But a long-term deal to a 34-year-old Center makes no sense, either. Overpay a bit for Sabonis, and you can probably get him. He's the last of the guys I think will be really interesting to watch in RFA, as I really have no idea what the value of a star 34-year-old is.
Joe Smith, Wizards - Productive enough player but on a rebuilding team - I don't think the Wizards want to commit a huge amount of salary to Joe, especially when they already have a better player ahead of him on a large contract (Juwan Howard).
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Eric Williams, Hawks - This guy has been nailed to the bench in Atlanta, so figure if he gets any really substantial contract offer, he's gone. But will he even get an offer?