I have been very satisfied with a) Liquid Dektol (actually Kodak Polymax) and b) Ilford PQ universal (but I would not use it for film). For cold tones I would also recommend Tetenal Dokumol.

In powdered developers my favourite is Ansco 130 (wonderful print colour and tone and it lasts for ages) and Dektol (a nice neutral/cold tone).

If you want to get into home mixed brews you should get a copy of the Darkroom Cookbook by Steve Anchell. It's packed with lots of practical advice.