My main problem with the maternity clothes is the sizing. Supposedly you order the same size as you wear pre-pg, but that didn't work for me last pg (with 2x). And this time I ordered the next size up (3x), and that didn't work too great either. So i guess I'm in limbo land.
My fave maternity top is Old Navy - but quality wise it is thin and cheap. But it looks really cute - the first one I got that wasn't cut like a sack. All of the maternity (and nursing) clothes I've gotten from ON have been very cheap quality. Super thin fabric, not even standard t-shirt thickness, more like you'd expect from an undershirt.
Stay away from Cafe Press - they don't have true plus-sized maternity clothes. Their 2x maternity is the same size as their Lg standard. Good thing they refunded me my money, or I would been on a rampage.
I ordered a couple long sleeve tops from JC Penney's this time, and I'm pretty happy with them. They don't fit right, being much too loose in the chest, but I suspect that's just something I'm going to have to deal with. They're not too tight through the belly, and that's the important part. I ran into the boob/belly problem last time too, since all the manufacturers seem to assume that plus-sized = DD boobs, and I'm only a C-cup (and a small C at that, not pg).
For pants, I just buy elastic bands, stretch pants, etc. I have one pair of dress pants one size up that worked really well for my bday dinner, but mostly I can wear my regular pants throughout pregnancy, so long as they have some stretch to them. My jeans are already packed away, but everything else is still regular pants. I have 1 pair of maternity pants with the stretch panel, and I can't make them stay up. Every time I move I'm having to hitch them up. And I had to hem about 4 inches off the bottom of them. So I'm guessing I just don't have the shape they need to stay up, since my lower belly doesn't round out.
My kids are opposite too - DS was born in September (our hottest month), so all my clothes from last time are summer. This time I'm due in May, so I may be hitting both winter and summer (unless we repeat last year, where winter lasted until July). So I had to order some long sleeve tops to round out my wardrobe. I have a cardigan that will work for pregnancy, and I just picked up a shawl/wrap (at Fred Meyer) that is warmer, that will do for when the cardigan isn't enough. I'm already out of my jacket, but my poncho still covers everything.