Ignoring all these Manny rumors until something more substantial is reported. No Andruw Jones please.
Next season, our starting catcher is going to be Varitek or a trade-ee/free agent to be named later. Our farm options, in terms of the ones who might be immediately ready, aren't palatable for a couple of reasons. But how about a year or two (or three) down the line?
Kottaras is an offensive catching prospect. Nothing more (unfortunately) and nothing less. He hits well for a catcher (.811 OPS in 522 MiL games) and has a good amount of power. He's caught 13 of 62 attempted base stealers this season (21%), and his harder-to-measure defensive skills aren't said to be polished. At 25, he's probably as ready as ever for a try at the ML-level, but I doubt he'll hit well enough to make anyone forget he's not very good defensively. Brown has been a slightly better hitter this season, but is at .730 by OPS in his career. He's a bit better throwing out runners (28%), and has better defensive pedigree. When/if Wake retires, Brown would likely jump up and be the backup immediately.
Wagner is a defensive catching prospect. 46% of runners thrown out this season, reported to have good catching skills otherwise (plate-blocking, pitch-blocking, etc.). He's a career .819 OPS hitter in the minors, but has struggled a bit in Portland (.758). Soxprospects (first link) has his most favorable comp as Brad Ausmus. Sounds right, all in all. Otness is basically filler at this point. Pretty old for AA, and he's got a decent OBP (.351) but a Lugo-like SLG (.348). Not great defensively.
Exposito might be our best all-around C prospect in the minors. His numbers against base stealers (23%) are hardly better than Kottaras, but again, according to Soxprospects.com, his catching tools are far superior. He has 17 HRs between two levels this season, in 303 ABs. The organization clearly thinks highly of Exposito. I take issue with their comp, however (Javy Lopez) as I don't think Javy was ever thought to possibly be a good defensive catcher (please correct me if my memory isn't right). Still's ML future, if he has one, is as a 1B/DH and third catcher. I highly doubt he makes it to the bigs even as a team's backup. Not good enough defensively, though his bat (.865 career OPS, .921 this season) has potential.
Everything below Lancaster is hard to hypothesize about at this point. Many are like Mark Wagner, but weaker offensively. Some certainly have higher potential, but very little experience and numbers for us to go on. If we go with an internal option in, say, 2010, it's likely Wagner would get the call and any offense would be considered a bonus. After that, Exposito is most likely, though he clearly needs refinement of his defensive and offensive skills. Luis definitely has the best chance of all our catching prospects, IMHO, at sticking as a starter in the bigs based on both his offensive and defensive potential. He is bilingual and reportedly (again, Soxprospects.com) very well-liked by his teammates.
Despite high hopes for those two, we could certainly use another potential starter in the system. Any of the Rangers young catchers would be good, and St. Louis's Bryan Anderson (speculation) could be available in the right deal, potentially.