I am 17 weeks along now and although not protruding in the belly area much just yet, my pants are not comfortable any more. A friend of mine showed me this trick of using a normal rubber band to extend the use of my normal jeans before having to buy maternity jeans.
I was pretty excited to learn that I have good tummy muscles according to my chiropractor, based on the theory I haven't popped out much yet. He guessed I was 11 weeks. I am looking forward to a magnificent, obviously pregnant belly though.
Good news for pregnant mums in Oz, I've found that JeansWest now have maternity jeans, and they are only $65 (instead of $150 from maternity stores). They even had 3 varieties, boot cut, straight leg and skinny.