Next step in diabetes medication

Patient: What would you recommend as a second medication for Type 2 DM in a newly diagnosed 40 y/o male?

Symptoms: My husband was recently diagnosed with Type 2 diabetes. He finally went to see his PCP after I checked his 2 hr post-prandial blood glucose and it was 599. He presented to his PCP the following day with the classic s/s…the 3 p’s, 40 lb wt loss, changes in visual acuity. His A1C is 15.7%. All of his other labs were pretty much as expected with severe hyperglycemia…triglycerides 1200+, liver enzymes just slightly elevated, creatinine 1.0, C-peptide WNL, UA positive for glucose, microalbumin elevated. Up until this point, he has been obese (6′ 1″, 255 lbs…now 217 lbs) and sedentary; however, he has no other co-morbidities or diagnoses.
He was started on metformin 1000 mg BID (said she didn’t want to drop him too quickly), a 90 gram carb/day diet, BG checks 6 times daily. He followed up with his PCP two days later. At that time his BG readings were all in the 200s. He was told to continue this regimen for two weeks and return to clinic for follow up. His BG have improved nicely and are now nearly all in the 130-190 range, pre and post prandial, and he is very compliant with his 30-45 gram carb/meal.
What would you recommend for a second medication at this point considering he is quite young and without any complications.