I used to go through seam rippers like candy, but then I found out there's actually a way to sharpen them. Considering I have one of those brass seam rippers that cost $15, I decided I was going to find out if there's a way to keep them sharp because I am not going to throw out a $15 seam ripper when it goes dull.
Get a set of jeweler's awls, they're like $5-6 on Amazon. I've got some but I'm re-organizing my quilting corner today and it's all the way upended, as soon as I find them, I'll snap a pic and post it, but all you do with the awl is run it one way along one side of the seam ripper, then repeat it with the other side. Go back and forth several times, test it on a seam, go back and sharpen again if it's not sharp enough. Once it's as sharp as you need it, you're good to go.