Grinding/Particulate Masks??

Do you guys use masks when grinding or doing any other type of steel fabrication? If so, what type do you use?

Depending on what I'm doing, sometimes I get lazy with putting a mask on. I've noticed that lately I'll be pretty congested for a day or two afterwards though. Plus, I'm sure breathing in the metal dust isn't good to a person's health. The masks I do have don't seal too well and fog up my safety glasses, which gets annoying. I figure it's time to be a little more proactive and find some decent masks that'll work. Short of a full on respirator, which isn't the most practical, what do you all use?