Do you use the Cokin system?
I do; I stumbled across a smoking good deal on Craig's List (50+ mint/NIB 'P' size filters, holders, CPOL, adapter rings for $40) a few years back, and grabbed it. While they're definitely not Lee/Singh-Ray quality, they're pretty good with the above-noted exception, and when I do drop or scratch one, it doesn't bother me overly.
I agree 100%. I have one Lee ND filter and several Cokin ND and GND filter. Lee's are very nice filter, but are MUCH more expensive. Cokin filters do have issues, but nothing that I can't deal with in post. Cokin filters, do, however, seem to scratch easier that Lees so you have to be extra careful when handling them. If I were making a living with landscape photography, I would likely go with Lee. But since I am just a hobbyist, I will take Cokin any day.