A different twist on geo splits is using the area codes to determin territory. This makes natural sense for an inside sales team that lives on the phone. It also pre-empts other confusing geo splits I've seen in the past. For example we have one client that gives within Route 128 Boston to one rep and outside the loop to another - very confusing. Also advisable to give each rep area codes that span the time zones so they have more call windows and can increase the liklihood of live conversations. 
 
 
 
This area code map is an absolute essential on the desk printout for any inside sales rep: http://people.csail.mit.edu/jrennie/areaCodeMap.png 
 

Great question and a very common one as of late. IncentAlign helps sales teams with exactly this problem. The software uses a combination of predictive analytics and market dynamics to strategically divide territories, accounts, and leads. A major factor in the allocation decision is a bid placed by sales reps on territory/accounts in terms of quota. Leads can also be dynamically routed based on analytics and a real-time bidding session. This way the best rep for the lead will get it based on their desire (input via a bid), analytical lead scoring, and preset management strategy. 
http://incentalign.com/products/