I have an FN HP SFS (Mark III) that comes with plastic grips. I would appreciate recommendations regarding replacement grips. The plastic grips are thin so that is not the problem. They are slippery and not attractive.
That's true (what Chris said), however I see them from time-to-time in the "classifieds" section of the various gun boards as well as e-bay. If you actively look for them, you'll probably score a set within a few days... I did.
Pachmayr Signature model rubber grips. As they go all the way around the grip, they give a good, solid surface to hold on to. Work really well when your hands are wet, as will happen when you are high on adrenaline.
For inexpensive grips there's a company that sells on Ebay with lots of wood grips for Hipowers. I picked up a set of kingwood grips for $14. They fit perfects and are very comfortable, as well as being very attractive. I had a set of their coco bolo grips that got broken but they were also very nice. Not the fanciest wood, but they fit and the price is very attractive.