I've been looking around for maternity clothes for ages and am finding it difficult...... most websites and shops that I go to have sold out of my size so everything's too big or too small. I ended up going to ripe and found some really comfy and reasonably stylish stuff there - especially jeans, they are great. Only thing is it's not the cheapest way to go.
I did buy some stuff off nextdirect but ended up sending it back as it was too big. I'd recommend if you order from them to stay with your Australian size (they say that the UK size is one smaller than Aus e.g. 12 Aus is 14 UK). I ordered 14 UK and it was definitely too big. Still the clothes came quickly, were heaps cheaper than anything in the shops here and were pretty stylish.
I reckon Metallicus and Witchery are good tips. I also found that Seed had a lot of stuff that I'll be able to wear for the entire pregnancy and while it's mostly loose and drapey it all hangs really nicely.