Nowadays IP has QoS, too. I work on QoS; for me, this means IP QoS.
In general, IP networks have performance metrics such as loss, jitter, capacity, and delay. Best-effort internet makes no guarantees about any of these. One can try to engineer networks that can control some of these parameters while not departing too far from the general IP paradigm.
There exist at least two ways of doing this: DiffServ (Differentiated Services) and IntServ (Integrated Services). Some tout MPLS and lambda switching as QoS techniques.
Internet2 works on implementing QoS using DiffServ within its QBone initiative. (And, of course, there are other people doing various neat things.)