I think the Big 12 has 4 options if they choose to expand:

BYU & Boise State

A North division of BYU, Boise State, Kansas, Kansas State, Missouri & Iowa State would be too weak compared to the Texas/Oklahoma division.  They'd have to create an East/West alignment or pair the schools together & zipper down the middle.

Cincinnati & Louisville

Same situation as BYU/Boise State but on the Eastern half of the US. Much less travel than the other options.

San Diego State & UNLV

Would be added to the south with the Texas schools - allowing the Oklahoma schools to rejoin their former Big 8 rivals in the North, Could add some exposure playing in large destination cities.

Memphis & New Mexico

Would be added to the south with the Texas schools - allowing the Oklahoma schools to rejoin their former Big 8 rivals in the North. Much less travel than the other options.

TCU & Houston

The conference is adament about not adding any more teams to saturate the Texas market.  As much as TCU & Houston would love to rejoin their former SWC rivals in an all-Texas division - it's not an option.

BYU Cougars, Provo Utah (Independant)

1.7 million people, 36th largest market (Salt Lake City + Provo)

8.1 wins/season past decade

75th ranked academically

averaged 64,000 fans in 2010, 100% capacity

coach makes $?

Boise State Broncos, Boise Idaho (Mountain West)

600 thousand people, 85th largest market

11.2 wins/season past decade

251st ranked academically

averaged 33,000 fans in 2010, 97% capacity

coach makes $1.5 million

UNLV Rebels, Las Vegas Nevada (Mountain West)

1.9 million people, 30th largest market

4.1 wins/season past decade

200th ranked academically

averaged 23,000 fans in 2010, 62% capacity

coach makes $500k

San Diego State Aztecs, San Diego California (Mountain West)

3.0 million people, 17th largest market

3.8 wins/season past decade

183rd ranked academically

averaged 25,000 fans in 2010, 35% capacity

coach makes $680k

Cincinnati Bearcats, Cincinnati Ohio (Big East)

2.2 million people, 24th largest market

7.8 wins/season past decade

156th ranked academically

averaged 34,000 fans in 2010, 97% capacity

coach makes $1.1 million

Louisville Cardinals, Louisville Kentucky (Big East)

1.3 million people, 42nd largest market

8.3 wins/season past decade

176th ranked academically

averaged 33,000 fans in 2010, 58% capacity

coach makes $1.6 million

New Mexico Lobos, Albuquerque New Mexico (Mountain West)

900 thousand people, 57th largest market

5.9 wins/season past decade

200th ranked academically

averaged 27,000 fans in 2010, 66% capacity

coach makes $750k

Memphis Tigers, Memphis Tennessee (C-USA West)

1.3 million people, 41st largest market

5.3 wins/season past decade

200th ranked academically

averaged 26,000 fans in 2010, 42% capacity

coach makes $750k