To elaborate, there are also ones specific to certain manufacturers. The universal one Rob linked to is okay, I have it too. The aluminum blocks that do the pushing wear over time and depending on the model it can be sort of a pain to do the front sight. MGW makes a very nice universal pusher for which you buy different attachments, but it's pretty $$. It all depends on how often you think you might need one. I broke down and bought the specific ones for HK and S&W M&P from MGW.
