Go ahead and get the letters from your 2 community college profs, but try to get at least one letter from one of your university profs as well. One way to go about this may be through a TA -- many times you will have interacted more closely with your TA since sections are far smaller than the lectures --if you have a TA you knew somewhat well and who you got along well with, see if they would be interested in writing the rec and if the prof could co-sign it. I did this for one of my chem classes and I think it worked out okay. Obviously the best scenario is to have the prof write it, but it will be very obvious if they don't know you well, and in my opinion it is better to have a strong letter from a "lesser" source than a vague unimpressive letter from a more major source.
Also, to all of you upcoming applicants -- once you start sending out letters of rec -- CALL TWO WEEKS AFTER THEY WERE SENT TO MAKE SURE THEY WERE RECEIVED!!!!!!! I had two schools that lost my letters of rec, and in one case it ended up costing me an interview essentially, because I didn't follow up on it quickly enough.