Looking for shoes I *can't* keep my lunch money in.

I would recommend you have a look at http://privo.zappos.com/. I have a pair and I find them really light and comfortable for walking around all day (and I normally have to wear orthotics to prevent my feet from killing me). They have a number of different styles, most of which are on the non-clunky side. They also seem to start at size 5 for women. They're listed on Zappos from $70-90, but I have seen them at that price or less in Canada.

I asked a near-identical question somewhere else a few weeks ago, and ended up buying these http://www.amazon.com/exec/obidos/ASIN/B001G0URG0/metafilter-20/ref=nosim/. They are insanely comfortable and can go for miles, go with everything, made with recycled car tires, and THEY ARE $30 WITH FREE SHIPPING. (The insoles are removable if that's a necessity, and they run just slightly small, so I'd recommend going with a 6.5 instead of a 6. I got mine a full size larger than what I usually wear and they're still comfy but just a tad loose.) Naturalizers were recommended to me several times as well, as were Danskos (neither of which I was too into). I do have a pair of Palladium ballet flats, though not the Kassels, and although I adore them the sole is kind of flimsy and they don't provide much support or cushion.

I don't know if they're as grown up as what you want, but I love my http://cdn2.tomsshoes.com/default18.htm They're the most comfortable shoes I own, and as a bonus, when you buy a pair (they're pretty much all at $50 or under), they give a pair to a kid in need. I wear them to my casual workplace. I also wear Asics Onitsuka Tigers, and think they look a little more polished than a bulkier sneaker, and they're more comfortable for me, too. I have black and white ones, but ones like http://www.zappos.com/product/126799/color/154983 are even a little nicer-looking.

Seconding Merrells. Don't be alarmed by their collection of clogs; they do have some cute styles. http://www.zappos.com/product/7487787/color/1897 is attractive, and are still fun while being a bit more polished. I have average-width feet, and they feel a bit wide to me, but you can read more info on the Zappos site. They also offer http://www.zappos.com/product/7505105/color/3, and there's a http://www.zappos.com/product/7463023/color/343 kind of thing, but they're $100 while the other two I linked to are $85.

Sometimes it's hard to find shoes that comfortably accommodate the extra layer of stuff in your shoes. If that's an issue for you, use Zappos (zappos.com) and search for "removable insoles". It's worth noting that most Keen shoes (except the sandals) have removable insoles.

My pair of Ecco shoes has lasted me 5 years and counting of pretty heavy usage, and are very comfortable for walking. They're not under $100, but they're the only non-running shoe non-dress shoe I've had for the last 5 years, and they're still in good shape. Mine go quite well with dark jeans, and I can get away with them and khakis too, which means I generally don't need to pack two pairs of shoes when I travel and need to look nice for something. Their women's selection is a little bit weirder than their men's, though.. maybe you could get away with something like http://www.eccousa.com/shoes/womens/casual/catch-tie/1857/detail.aspx though?

I'm in a similar boat (grad student, trying to age-up my wardrobe), only I was trying to go from flip-flops/sandals to something equally comfortable. Recently I've fallen in love with simple ballet flats like http://www.target.com/Mossimo-Supply-Co-Odell-Ballet/dp/B001HXF3FQ/qid=1241059599/ref=br_1_1/184-6669189-7958363?ie=UTF8&node=13827221&frombrowse=1&rh=&page=1. I've seen much more expensive alternatives out there that will last much longer, but for $13, you can afford to replace them several times over and never feel the ding (a major plus to me, living on a grad student budget). These pull even jeans and a t-shirt together and make me feel way fancier while still feeling comfortable than anything I've found before.

I don't know much about specific shoes, but I stick SuperFeet insoles in all my shoes. Gives me good arch support in all my shoes (if that's the comfort issue).

you don't have to stop wearing sneakers, just wear more polished sneakers—lots of very stylish people of all ages in nyc (designers, architects, etc) wear asics onitsuka tigers, pumas or adidas to work. they look great, some sleek enough to wear with suits, and you can walk miles in them.