There are many options in maternity shirts from Old Navy. There are tanks for layering, nursing, or for use when the weather is warm. There are also long sleeve and short sleeve maternity T-shirts in many stylish colors and patterns. For those looking for a special occasion outfit, or something that can be worn to work, there are also tops that can be worn with dress pants or skirts.
I believe that it is worth investing in maternity jeans early on in your pregnancy - they are so much more comfortable on your expanding waist, even with a small bump so why wait? Also compared to normal jeans they will have limited wear (although I have friends who still wear theirs for a Sunday roast). You will most probably be wearing them for a while once the baby has arrived too - so get some you love.
I did all of my maternity and nursing gear shopping here and absolutely love it! Thyme Maternity across the street seemed to be the same in quality but has a smaller selection and is a bit more pricey. I have alway gotten great service here and there always seems to be great sales. In the month right after I had my baby my husband went to get me nursing tanks but the sizes he got were too big and when he went back to exchange them he said is was super easy and they were incredibly helpful. I have also gotten nursing shirts as gifts from there and had to exchange sizes and the gals were so nice about it. In some stores you sort of get the eye roll when you have to go return or exchange things or it even feels like the sales people are trying to make it difficult for you, but that has never happened to me here! Great place to shop :)