There are viruses, like VZV (chickenpox), Enterovirus C (polio) or the measles virus, which have very low replication error rate and therefore their genetical complex is considered stable. As the result, one vaccination by alive attenuated vaccine is able to provide lifetime protection.

Some viruses, like type A of flu virus, are mutating quickly enough to make vaccination inefficient in the long term. It only will be effective for short periods, and only if the researches will make a right guess about future epidemic strain.

Others, like HIV, are displaying so high replication errors rate that even short-time effectiveness of vaccination is literally unreachable. You may develop a vaccine but it won't be able to protect anyone, because the blood stream of infected individual contains ~10^10 variations of virus which are unlikely to match a strain used in the vaccine. This is why the so-called HIV vaccine researches are nothing but fraud. These guys are spending money to develop vaccine which won't work by definition. Killed HIV vaccines won't work because they wouldn't match actual strains of the virus. Alive attenuated HIV vaccines won't work because the vaccine strain will mutate until it will become strong enough to cause the desease.

P.S. You can see a funny analogy between HIV, its animal equivalents (FIV, SIV, dozen of others) and polymorphic computer programs. HIV/SIV/FIV mutation rate is so high that it functions on the verge of self-destruction. Therefore, this family of viruses is clearly the best sample of precious engineeging work which nature may provide. Some people would consider it as a living proof of the God existence.