I'm specifically looking for advice on pants. I'm looking for brands that can be washed easily in the sink and dry overnight, but can also be paired with a nice shirt and be fine for restaurants. Also just looking for other tips in general regarding clothing. We'll be in London, Paris and Belgium during the end of July through middle of August.
Check out Tilley's. Although not cheap, their travel pants are of superior quality and can absolutely be washed and dried overnight. I particularly like their "AdventureCloth Classic" pants, which I basically wear every day when I travel. www.tilley.com
In general fabric not brand determines how quickly an item dries. Cotton takes a long time to dry. Jeans take forever. There is no such thing a quick drying cotton and any seller claiming their cotton pants are quick drying is lying. Synthetics dry much quicker. Doesn't matter if they are Walmart brand or the the most expensive as long as they aren't too thick they will dry overnight. For items you already own if you don't know the type of fabric (or even if you do), do a test run. Wash them by hand and then the next morning see which ones are dry and don't look like crap. Darker colors tend to hide dirt and wrinkles better than lighter colors.
You might also try Ex-Oficio and TravelSmith catalogs.
REI has a nice line of travel clothing under the Explorer brand. My favorite travel pants is Outerrim from Sam's Club but have not seen the pants in a couple of years. I would avoid all cotton and all nylon. The newer synthetic blends are terrific. I do have one pair of pants with a 30% cotton blend but would go any higher than that. I keep to browns and tans with light color shirts and find it very comfortable. All of the pants and shirts have hidden pockets or pockets secured with zippers or a double closure system.
One way to stand out as a tourist is to wear the expensive "travel" clothing. Except in upscale places most people that I saw were wearing everyday dark colored polyblend pants.
My two favorites, right now, are Dockers D3 Microfiber pants and Izod golf pants (also microfiber or polyester). Both can be purchased at Macy's or online and are on sale often enough to get a decent deal before your trip. Retail prices are about $60, but I've never paid more than $40. Here's my visual pack list: http://www.polyvore.com/cgi/set?id=1440268 It's built with September north of the Alps in mind, you will want to go lighter for July/August. Don't forget the rain shell though, it can rain anytime (especially in London and Belgium).
For quick drying, I've had great success with Ex Officio. Unfortunately, they stopped making the cotton/poly blend I liked so I've been using Royal Robbins as an alternative.