Hi eyespy,
Oil based primers work really well, they are a bit more of a pain to put on a whole wall though and are very smelly.
I use the acrylic 3 in 1 primers such as Bristol All Prep or Taubmans 3 in 1.
It is a good idea to etch the surface you are going to paint with some sand paper to allow the primer to stick to it extra well.
Bronwyn.