Before having a child I always felt guilty over the smallest things - now that I have a baby it's even worse, sometimes affecting my mood. How do you deal/cope with mommy guilt?

I work full-time and feel guilty for leaving my child, yet when I'm at work I feel guilty b/c my work is slacking (not spending as much time at work as I use to). I also feel guilty when I read things that other mommies do that I didn't/don't do that I maybe should/shouldn't do. I try to tell myself that as long as I'm doing my best - then I shouldn't feel guilty but it's hard to get through my head.

I know Mommy Guilt will always be there but hoping for some help, tips, insight on how to not let it ruin my day.