Let me start with a warning, check to make sure the online school is fully accreditted. There are many online universities that say they are accredited, and they might be, with some odd international accreditation, but it is of no use in the U.S.
In choosing an online university you might want to consider cost and/or the reputation of the university in the business world.
Here is some research I did when choosing an online university on pricing (all prices are per credit hour):
First, two schools with great reputation that are traditional universities, but offer online class work:
University of Massachusets - $314
Penn State - $446
University of North Texas - $211
The rest are online universities:
Kaplan - $353
University of Phoenix - $325
Ashford - $262 to $337
Aspen - $250
Butler - $190
The pricing is in case you current employer pays for tuition.
Good luck with your degree pursuit.