Marshrutnis (minibuses) from Yerevan are inexpensive and will take you to Vanadzor in a couple of hours.
Taxis are available, and practical for visiting sites in the nearby area. Agree on the price beforehand, to avoid being scammed. The ones running on gas are less expensive than those on petrol. Expect to pay about 100 Drams a kilometre (summer of 2007), plus a starting fee.
Marshrutnis (minibuses) are, as always available. There are also gas-operated buses.