I thought I'd post a few thoughts about maternity clothes here, in case anyone was considering in investing in some. :)
When I first started gathering clothes, I abhorred the pants with the big panel across the belly. Oh my gosh. Who wears those? So, everything I bought for myself, I made sure they were the low-rise, below-belly type. However, I've found two problems with those. First, the 3-inch elastic band can twist and fold inside the fabric. This is really frustrating, though liveable. Second, as I've gotten bigger (just recently at 6-7 mos), the same band has a tendency to fold over and put pressure on my belly, which is not comfortable at all. So, I've pulled out a few of the big panel pants. And gagged every time I put them on. I mean, really, is there no other way to be comfortable? And even these aren't that comfortable. Yes, the elastic doesn't double over and hurt me, but now the elastic is at the top of my uterus (or directly across it), and that still isn't that comfortable. But I admit it is better.
The best pants I've found are the knit gauchos I wear for my belly pics. They're super-comfy, will stretch to whatever size I am, and put absolutely no pressure on my belly. As a matter of fact, Motherhood Maternity has a line of pants with the "secret fit belly" that I think are basically the same as my gauchos. I haven't bought any because I don't really need more maternity clothes, but they would be my top choice if I were to buy pants. And, for those of you like me who hate the idea of the full-belly coverage, you can fold the panel down.
Something else I've found invaluable are my workout shorts: one pair from Target and one pair from middle school gym class. They're stretchy and comfy, and will definitely make it through the entire pregnancy--at least through shorts season. Plus, they're shorts I already owned, and will continue to wear after the pregnancy.
I've outgrown about half my underwear--some pairs are just stretchier than others! I haven't found the need to buy maternity undies, but I do see how some seamless ones would be nice and comfy. And they wouldn't have to be maternity, either, just regular ones from Wal-Mart or wherever.
I've pretty much outgrown my bras. For whatever reason, one pre-pregnancy bra is still hanging on (with the help of the bra extender), but I think it's time to retire it and move to a larger size. The first time I moved up sizes, I added 2 inches and 1 cup size, and I think I'm going to have to go up again one more time (both inches and cup size) before I hit nursing bras. I've read that when I buy nursing bras (if I buy before baby), I should add a cup size to account for my milk coming in after baby's here, so I may be changing sizes one more time, at least! I've kept two "day" bras in constant rotation, and one comfy sleep bra.
I don't really have a lot to say about shirts. My favorites have been t-shirts that are snug enough to show off even the smallest baby belly. Otherwise, they feel like circus tents until about the 7th month. The crossover type shirts are very popular, and usually very low-cut, so black and white camisoles have been a good investment.
And dresses have been a godsend in hot weather. When you can't wear shorts (church or work), dresses are a way to keep cool, and there's no elastic around my waist! My favorite are the kind that stretch around the belly and then come back to normal shape around my legs--showing off the belly. Others just hang off straight off the belly, making it quite breezy below, and also making an already-self-conscious prego feel like a small whale. (I'm sure they look fine, and it's just me, but I'm just warning you.) If you're pregnant in the warmer months, I'd recommend getting some casual knit dresses, even if you won't need any for special occasions or things like that.
Overall, maternity-wear should be fun and comfortable, should reflect your style, and should make you feel pretty at a time when your hormones and emotions may tell you otherwise.