It's now been reported that the Big 10 will offer bids to join to Missouri, Nebraska, Notre Dame, and Rutgers. If Notre Dame accepts a bid will be extended to a currently un-named school to bring the total to 16 but if Notre Dame rejects (which seems likely), they'll stick with 14.
If ND rejects the offer (which seems likely with the Big East still being able to exist giving them a home for their other sports), the Big East will probably only add one more football playing member to keep the league at 8. So who will it be?
The Sun Belt has consistently good teams like Troy and Middle Tennessee is usually alright. WKU is the newest D-1A team and the Sun Belt will soon add South Alabama. In all honesty, however, the only Big East level market is Mobile and USA isn't even officially an NCAA team until 2011 and won't be D-1A until 2013.
The MAC is a strong enough league but are the markets really big enough? Buffalo is a large enough market but they only reason they're football team is semi-relevant now just went to coach at Kansas. Temple is in Philadelphia but it's Temple. They were Big East and they were a doormat then. To be fair, Al Golden is doing a nice job with their program but they are the black sheep of the Philly sports scene usually and didn't/don't draw too well.
The Big East could just dip into Conference USA again. It's not the most appealing (keeping Rutgers would be better) but it's not the most unappealing either. Common tossed around names include ECU, Memphis, Southern Miss, and UCF.
Despite the level of play coming up in the Sun Belt, C-USA and the MAC are still perceived as a better product so the Big East would be better off taking a team from one of those two. I haven't heard any names from the MAC mentioned and as I said above their markets aren't really Big East level so that leaves C-USA.
ECU gets the Big East into the Carolinas, an underrated recruiting ground that, while currently accessible, becomes easier to draw kids from when your team and conference are regularly on TV in the area. While Greenville itself is not the biggest TV market, with alumni across the Carolinas, its games are carried across the majority of both states and some in surrounding states.
Memphis gets the Big East into the Tennessee, Arkansas, and Mississippi region. Fertile recruiting ground and a sizable TV market. It's tough enough to steal a kid from the heavily SEC-laden area but that would be easier with a team in the area. This also rekindles a Memphis-Louisville rivalry.
Southern Miss gets the Big East a hold in the Gulf Coast region. The Hattiesburg area is a good size (a July 1, 2009 estimate puts the population of the Hattiesburg metropolitan area at around 143,093). Their alumni base spans the entire Gulf Coast and, yet again, provides access to a great recruiting area.
UCF gets the Big East into Florida ... oh wait they're already there. Doesn't matter, it's always good to improve your presence in the Sunshine State. Adding UCF would help the Big East in several ways: it helps recruiting (two Big East schools versus one means double the name exposure; that's why the ACC wanted Miami so badly), it's a rivalry (USF might not see it that way anymore, but they would if beating UCF helped them win a conference championship; also why the ACC wanted Miami), and Orlando is a huge TV market (you gain a huge chunk of viewership in the central part of the state and that helps compete with the UMs, UFs, and FSUs).
If it were up to me and I was presented with that short list, my order of expansion candidates would be UCF, Southern Miss, Memphis, and ECU. I think a slight edge goes to Southern Miss over Memphis.