I was just barely working on a pacman clone about two months ago... turned into mostly just research. It turns out the ghosts follow rather simple patterns between two modes (spread out / attack) which turn into complex behavior, mostly due to how they interact with each other.
was the best guide I found, its brilliantly in depth and covers more behaviour than I ever realised, like how the pacman turns corners. Pity I only found it after I mostly finished it.
I didnt realise the ghosts has fairly complicated strategy, should be fun to implement now the mechanics are mostly done.