I need a bag to carry gym stuff and work stuff.

I do carry my workout clothes and shoes to and from work. With a lunch, laptop, newspaper and an occasional book, there isn't much room for shoes and clothes.

How do you commute? If it's by car, then I'd just leave the gym bag in the car and switch things out when they get gross. If you're commuting by public transit, I'd seriously consider getting a messenger bag. Timbuk2 is the classic brand, and their bags are very sturdy and some are quite large (I regularly use mine for overnight trips). However, I'd be kind of grossed out by keeping my gym clothes with my laptop and lunch, but I guess you could use plastic bags to keep everything separate.

http://www.ospreypacks.com/Packs/TravelCouriers/Transit/ bag by Osprey is work-appropriate, has great interior organization, lots of space, a padded laptop sleeve, and enough structure that it's easy to look around inside without the bag collapsing on itself. My husband just got one for his bike commute, but it would also work great on the train or in a car. I think the colors look a bit more sporty and the black a bit more office-y. I have a great bag by Sherpani (bag is called Flora Major) but it doesn't have the structured sides so it's harder to keep organized. Also it has a floral lining, which doesn't sound like your style. I would recommend carrying a plastic bag wadded up in your messenger, so you can stick your gym clothes in it post-workout.

I use the http://www.staples.com/office/supplies/StaplesProductDisplay?&storeId=10001&langId=-1&catalogId=10051&partNumber=634619&cm_mmc=GoogleBase-_-Shopping-_-Office_Supplies_%253E_Computer_Backpacks_-_-634619-GA-7306-06F00&ci_src=14110944&ci_sku=634619. It has a separate compartment for your laptop (with a snapover harness to keep it upright), plus two HUGE additional compartments for clothes, shoes, books, whatever, and side pockets for keys, sunglasses, iPod, etc. The thing seems to expand endlessly and has Camelbak-style padded vents on the back for ease of carriage when you overstuff it. I routinely pack my computer, change of clothes, lunch, bike padlock, etc., into mine every day for my 23-mile bike commute, and it's never failed me. Plus, it's machine-washable.

For a few folders, sneakers & gym clothes the bigger Tumi expandable cases, http://www.tumi.com/business_laptop/briefcases/category_search/expandable_organizer_leather_computer_brief/product_detail/index.cfm?modelid=108214, and knockoffs will just do it. Make sure you get the expandable version. But now I use a http://www.mountainhardwear.com/Product.aspx?top=1246&prod=2058&cat=1272&viewAll=False bag, not super corporate but it depends on your culture.

I use a timbuk2 with a laptop sleeve. Ideally I'd get the largest size possible, but I have the 15" (sleeve size) and it works fine. You can get an http://www.timbuk2.com/tb2/products/laptop/herringbone-commute. Timbuk2 bags aren't pretty (I hate the logo and two tone design in particular), but they are damn tough. I'll probably reluctantly buy another one after my current one dies (4 or more years with almost everyday use and still going strong).

er, I should mention my 15" fits shoes, shirt, shorts, a bottle of water, a book and a laptop. There's still a little room to stuff crap in it with all that in there.

http://ask.metafilter.com/97678/I-need-a-bag-to-carry-gym-stuff-and-work-stuff#1423362: "I would recommend carrying a plastic bag wadded up in your messenger, so you can stick your gym clothes in it post-workout." If you're near one, Apple Store bags are great for this purpose. The drawsting works well and the plastic's thick enough that personally I've even occasionally rinsed it out and let it dry without making it go goofy.

I have had a http://www.pacdesigns.com/firsts.htm for the past four years. It has proven to be not only sturdy to the point of indestructibility, but comfortable and large enough to accommodate way more than any other bag I own. They're kind of pricey, but if messenger bags are your thing, a PAC may be the last one you ever need to buy. If you go this route, I'd advise you fork out a bit extra for one or more of the 'options', particularly the 'X-strap' and the laptop bag.