There are a number of taxi services which are based outside of Davis but will give rides to the Sacramento Airport or between Davis and Sacramento. The bulk of these are members of the Sacramento Taxi Association (STA) and/or the Sacramento Independent Taxi Owners Association (SITOA). SITOA drivers have purchased one of a limited pool of "medallions" which give them the right to operate a cab in Sacramento. The are also licensed (or should be) to do airport pickups/dropoffs. Since it's a bit of a drive for them to come to Davis, though, most won't do intra-Davis rides. That's OK, though - there are a number of local options.
"Bk Cab Airport Only" - 916-222-5200 - www.taxidavis.com
Kmm Cab Co (also known as Davis Taxi) - 916-821-4471 - www.davistaxiservices.com