Two that I might watch would be Tennessee which has been training through most of the early season meets and George Watts will have them ready at Regionals. The key will be Tim Kelly running up to his 8:49 steeple type potential which he will later this season. Gildea is having a coming out party to speak of and with Cloutier, Defillippis, and Bell taking form. Watts will have them ready to make a run at regionals.
Of further note I think Arkansas Little Rock has a stellar team that has yet to run close to its potential. Arkansas state champ Eric Gross has been running with the flu but is a sub 25 min 8k guy. Their leader Brent Corbitt is having a good senior campaign. The key is to get Gross back to full strength and to get the European tandem shokur brothers who are two studs running up to full potential. All have been training VERY hard and when they back down they should have a great run at regionals as well. Kirk Elias is a very smart coach who will get the most out of his guys.
The key to the above list and my two "dark horses" is the injury/sickness factor. One guy goes down on any one of the teams that are listed in "RED DRAGON's" list and the whole thing changes. One can only see how the loss of Dathan has changed the face of the CC season for CO.
The great thing with regionals is that every year you have a favorite that has an off day and won't make it and an unranked team that runs well and gets in. It all depends on who shows up the day of the race! You gotta love it!