I wore something from www.tiffanyrose.com when I was matron of honour at 8 and a half months pregnant. It looked good and was comfortable too, which was a not insignificant factor at that point. They were happy for me to order several dresses to try on and decide which to keep, refund on the ones I didn't keep was no problem.
So sorry everyone, I went out for dinner and haven't had chance to reply yet! Thank you, I'll look at Tiffany-Rose, and check out EBay. Ideally under £150ish, I have a few weddings coming up. I'll also try on a few different lined dresses to see if any 'normal' ones fit, I'm not actually that big I think, so may get away with it
Might not be to your taste but I had a maxi dress to wear to a wedding from Dorothy Perkins when I was pregnant. It was a jersey type material but looked good. Didn't go to the wedding so wore it to an afternoon tea instead. Was comfortable too and it wasn't a maternity dress.
Very pleased with the dress I got, it's perfect for a wedding and was in the sale so not expensive. I found their sizing guide to be spot on too - which is a relief after days of trawling website for stuff!