The general rule is to get the best enlarging lenses you can afford - or maybe slightly more expensive ones. The Ctein book offers excellent advice. Read it. The 50/2.8 EL-Nikkor is an excellent lens, and other lenses are often compared to it. For other lenses, look for 6 element lenses from the major manufacturers - Nikon, Fuji, Rodenstock, Schneider, etc. You can definitely tell the difference between prints produced with a 3 or 4 element lens and prints produced with a good 6 element lens.
My current inventory is a somewhat mixed lot, but they are the kind of lenses you should be looking for: 40/2.8 Apo-Componon (Schneider), 50/2.8 EL-Nikkor (Nikon), 80/4 EL-Nikkor, 105/4 Apo-Rodagon-N (Rodenstock), 135/5.6 Rodagon, 150/5.6 Rodagon-G, 300/5.6 Rodagon-G.