I have a Koko one from Amazon, there's a ton of different styles. It's cute enough to carry on it's own like a purse if I'm using for C's milk or something, but also fits into my work carry-all bag. It was also under $20, so pretty reasonable.
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Mine isn't super insulated (just a light lining inside) but I love, love, love it. It's sturdy canvas and says "Lunch" on both sides just in case there's any question, LOL. Anyway, it's really cute and I got it at CB2 though you can buy it online. It's made by Fluf and the best part for me is that it is washable since I'm kinda messy about lunch for some reason.
Re: Insulated lunch bags
I just got one from 31, and I love it. It's roomy, easy to wipe out and adorable.