T.R. Sullivan has a rundown of free agent starting pitchers this offseason. The only group that likely matters for the Rangers, though, is the final group -- the guys who will be getting minor league deals with NRIs. The Rangers are, I think, very unlikely to go out there and spend money for a veteran free agent starting pitcher, particularly since most of them would require a multi-year commitment.
And given the guys the Rangers already have to sift through for the rotation next year, I don't think it makes a ton of sense to go spend money on a Jon Garland or a Ryan Dempster.
Over on the Tigers website, there's more talk of Detroit's interest in Gerald Laird and their lack of pitching necessary to make them a front-runner for him.