I agree with daydreamer254. The weight that some programs put on the LORs can be radically different than others. My program required 3, but I only had to have one from faculty (it just didn't seem like that put THAT much weight on LORs, to be honest). Some programs put much more weight on GPAs (and you have a good one, so I wouldn't worry) or the GRE (some don't require it); some don't really seem to care about those at all. My program said the two most important things about my application was my SOP and another essay I had to write for them.
Like daydreamer254 said, it doesn't hurt to ask. The one prof I did ask, and who did write my letter, said that he'll upfront tell students no if he doesn't feel like he can write them a strong letter. He won't waste his or the student's time. When I asked, I asked if he would be "comfortable" writing me a "strong" letter so as to give him the option to say no if he didn't feel like he could.
I don't know how much time you have left until you graduate or are applying to grad school, but if it's awhile, you can always try to get to know the profs now. I transferred my junior year to my current university, and as soon as I knew what prof I wanted to write my letter, I made sure to go and see him during his office hours and took more than one class with him so that he could write me a strong letter. However, like daydreamer254 said, they don't need to know you that well and vice versa. When I asked my prof, I gave him my resume, SOP, and another essay for my grad school just to give him more information about me, why I wanted to apply, what I wanted to do once I graduate from grad school, and a bit of information about my previous work. He said that helped a lot. I think it's also a good idea to tell the prof why you're choosing him/her. The reason I chose my prof is 1). He graduated from grad school from a top 5 and 2). I do so much writing for his class (and do well), and I bombed the GRE AW, so I really asked him to highlight that.
Also, getting some from employers is a good point. I already work in the field I'm going to grad school for, so I asked the director of my place of employment and my direct supervisor (who also happens to be a professor) to write two for me. Employers may not be able to speak about your academics, but they can speak about your personal character, which says a lot, too.
Good luck!