I just wanted to add a hint. Don't buy anything without trying it on. For some reason this time around, I'm having a hard time getting tops to fit me. OK, not for "some reason"--I'm HUGE in the tummy (DS4 is so afraid I'm about to explode) and haven't gotten any breast increase this time around. My OB says that is very normal when you get pregnant right after you just finish nursing. No more nursing ****, but no preparing because your ducts are actually mature. I just need to watch out after the baby is born. But that is WAY too much info.
Another hint. Don't buy anything before you need it. You DO NOT know how your body will change. PG#1--prepregancy size through out my whole pregancy, put on a total of 31 lbs. My hips never spread, only my tummy & breasts grew. Back into my clothes by 4 weeks post partum. PG#2, I put on half the weight (15 lbs) and outgrew all my left over maternity clothes by the time I was 5 months along. The same things I wore at 9 months the last time. My butt was huge, my hips spread, I had 2x the breast size. Baby was about 4 months old before I fit back into my clothes. 8 months into PG#3 (so far I've put on 38 lbs), bottoms I'm still wearing pre-pregnacy size but I've gone up two sizes on tops to accomadate my tummy. Just buy a little all the time. You'll never get bored/fed up with your clothes either.
Lastly, a great place to get maternity clothes that hasn't been mentioned--friends. Those who are done with their families may still have stuff on hand and those who are still working on their families may lend you their stuff they've put away. Just be sure with anything you borrow to return it in the same condition you received it; if anything is ruined, offer to replace it.