I don't have recommendations other than Built because I have carried a Built bag for four years and it still works just as well as it did when I bought it. There are a variety of colors and sizes you can buy, which is nice.

I have a Built bag and I love it!!! It took me so long too to find a decent lunch bag!

My perfect lunch box would be flat - like a little brief case or a laptop bag, so that I could slip it into a back pack. Also it would zip up completely to keep spills away from my work. Something like this:
http://www.amazon.com/Wildkin-33501-Fern-Green-Lunch/dp/B0067QYHHI/ref=pd_sbs_a_8

But maybe a little slimmer.

I love when lunch bags have a hard interior- in case I have squishy stuff...at least 3 or 4 people in my office (including me) swear by California Innovations lunchbags. I got mine at walmart: http://www.californiainnovations.com/lunch-bags/frontpage.html

Going to have to +1 the Built bags. I have been carrying the same one for 5+ years and it's still going strong. Zipper still zips, it can go in the washing machine. It's big enough to hold an ice pack and a good quantity of containers - plus flexes enough to get it closed even if it's a little TOO full.

I went through this as well when I was in grad school and working part-time. I ended up purchasing a Laptop Lunch without the containers, just the thermal outside. It was slim enough to fit in my backpack along with my school materials and can packed pretty tight with food.

Ju-Ju-Be has a small insulated bag called the Fuel Cell. It was originally designed for moms & babies but it's super for adult lunches, too---it comes in tons of pretty prints, zips securely shut, has an anti-microbial lining, and is machine washable. Perfect for keeping it clean and smelling fresh. And when it's empty, it folds completely flat to save space.

As a student myself I love the Rolltop lunch bag from built. It fits just lunch or a hold day as you can choose the size. The handle is also a clip so you can attach it to your bag if you need more room for books and other essentials. http://www.builtny.com/rolltop-value-pack-prod.html

Bento boxes might help you out: http://www.laptoplunches.com/

The bags I've had always get filthy. I love my Tiffins. Light and durable, seal nicely. They can go in the dishwasher and people at work ooh and ash over how cool they are.

I had a lunch bag similar to this one, and while it doesn't fold flat, it is large and will hold items flat. I used to work a 12 hour shift and this held my lunch, dinner, snacks, and because of the drawstring top, I could put my nalgene in there.
http://www.igloo-store.com/detail/IGL+DRAW+9+PINK+BL

I forgot to mention another reason I like my Built bag. It's made of neoprene, which is more flexible than the typical insulation fabrics. If you carry a backpack, it can be really hard to shove something rectangular into the little space you have leftover. Since Built bags are more flexible and are usually round, you don't have to shove any corners into a tight space and the fabric bends and folds enough to give you more chance to fit it into a backpack.

I, too, as a graduate student carry a BUILT bag around. It washes up really nicely, and like others have said, is flexible to hold a large capacity, and be shoved into tight spots.

My only complaint is that it doesn't keep anything cold. It's not insulating, and so I either throw in an ice pack, with, after the meal, still retains some bulk, or I freeze my meal and then throw it in the bag, or....I just don't worry about it. I do wish that things would stay cooler inside, though.

I use an oilcloth bag - bought it on Etsy a long time ago, but it would be easy enough to make one yourself if you sew. It's shaped like a paper lunch sack and has a velcro closure up top. Holds enough, easy to clean up, folds flat, and even insulates a bit.

I also love Built and recommend the "relish" lunch tote --- it's the largest, as I understand. I've used it for two years now for baby bottles/food when on the go with my daughter and it's held up very well. True you need an ice pack to keep things really cold, but if you are carrying things like salads and sandwiches, I expect the bag itself would keep your food fresh until ready to eat.

Also, eBags website has a lot of lunch totes with lots of customer reviews --- could be very helpful. I bought my Built there but I also have an eBags brand perfectly sized for carrying frozen meals --- it's basically an insulated rectangle.

Also love my Built bag because 1) it expands nicely if I'm toting a big salad in a plastic container 2) folds up and rolls to fit in my purse after lunch 3) washable 4) a range of cute designs.

I had a Built in college and LOVED it, but no matter how many times I washed it, I felt like it acquired a kind of funky smell after a while (probably from a spilled dressing at one point, but it won't go away!) Any thoughts?

My husband and I both use the Built bags, and they works amazingly well, as very good looking, washable(have been washing mine for 2 years and no stitching has come undone), they insulate very well, and can expand and fit a lot of things.

I use a cooler bag that came in a gift pack from the Cuba Cheese gift shop - and I love it. I've used it for years. I checked the site and its still available www.cubacheese.com. Go to Gourmet Gifts or search for "The Six Pack". Its $39.00 filled with meat and cheeses. The horseradish is to die for, btw!

It is 6 in deep x 9 in wide x 6.5 in tall. Its insulated, zips, wipes clean and folds flat. Its square and I can pack a bunch of food in here...but its not tall. A thermos wont fit.

When I was measuring it, I noticed that the zipper says "the original koozie". So I googled that and found that you can find this same size really cheap on Ebay if you dont care about the product marketing. Less than $5.00

There is also a "Koozie" that I found online that is a 12 pack cooler bag and is slightly taller.

I have the lunchbox from this set. They were selling them for $5 last year at Home Goods. It's very sturdy and it's lasted really well. I've had it for about a year and a half now and it's still going strong. I like that it stands upright on it's own so my containers don't get turned upside down in transit. I'm a teacher and graduate student so like you I'm often packing one or two meals plus snacks and this lunchbox has plenty of space.

http://www.amazon.com/Sachi-Paisley-Insulated-Tote-Set/dp/B005F5LH2U/ref=sr_1_29?ie=UTF8&qid=1363220052&sr=8-29&keywords=sachi+lunch+box