I've been looking around at yard sales and such for a deal on an old road bike for commuting (trying to get a $20 deal). I was wondering what are some good brand names to look for?

I don't think you can rely on brand names, unfortunately -- lots of manufacturers have made bikes with a great range of qualities, and there are lots of possible brands that could be on good bikes. I think you're better off getting to know what makes for a quality bike so that you can appraise whatever you happen to find. Luckily you have lots of good resources available to you -- check out the Classic and Vintage forum here, and do a search in its archive for similar queries. I also found the Vintage Lightweight Pricing Guide on Sheldon Brown's site to be really helpful for getting a sense of what might be out there, although it's out of date and somewhat geared to "collectibility". That said, I've never been too lucky with yard sales. Don't forget craigslist, and see if your area has a recycled bike co-op -- the latter has the advantage of coming with some help setting up and maintaining the bike. Good luck!

CraigsList is your friend.

Decent brands to look for:
Bianchi
Bridgestone
Nishiki
Centurion
Miyata
Trek
Univega

Other brands where there are some gems, but a whole lot of mass produced, lower quality bikes:
Pugeot
Raleigh
Schwinn

Don't ignore the lesser known brands, either:
Kabuki (produced by Bridgestone?)
Shogun--I got a great deal ($65) on a Shogun 600: lugged, butted steel frame, shimano 105 "Golden Arrow" components, in good working order.

Too many small, good brands to list. The usual sign of a decent quality frame that can show no matter how bad the wear on labels and paintwork is the use of investment cast rear dropouts. These have a moulded shape in contrast to the stamped sheet-metal dropouts of cheaper bikes.
With lugged bikes, cheaper ones have a large step in thickness between lug and tube, better quality ones use thinner lugs or have a graduated reduction in thickness from filling the lug.

I love Peugeots, but would hesitate to get one because of their "French Threads" which are a slightly different pitch than others. That makes it harder to find parts that will fit. Japanese makes and Chinese made ones should have more universal components.

Don't forget estate sales. There tend to be more old bikes that weren't too abused or used. Estate sales are better than garage sales, because at garage sales, people select their unwanted items. Estate sales have a wider selection.

Let's not forget Specailized!

Older, main-brand mountain bikes from the 1980s and early 90s (no shocks) can make durable cheap commuters once you slap on a pair of slicks; most came ready for fenders and a rack too. Specialized, Trek, Cannondale, Trek, and others made bikes like this. Lots of them are available on Craigslist.

Panasonic
Univega +1
Puch

Alot depends on what you mean by "good". I commute on a '77 Schwinn Le Tour II and it makes an awesome commuter. Yeah, it's heavy (30+ lbs.) but it can take the abuse of railroad tracks and potholes without complaining. Probably no heavier than that era of MTB and I like the more aero position (80% of my homeward commute home is into the prvailing wind so 10 - 25 mph headwinds are common). Oh, and it was pulled out of a dumpster so total cost was under $50 and a few hours work for a solid commuter.

Raleigh - I have found that damn near anything raleigh is a good bet. Some have weird threading but if you get a fairly complete bike you will be fine.

Schwinn - There are some wack-a55 schwinns out there and there are some real beautys. I have one of the really awesome ones.

Panasonic - nothing bad to say

Miyata - Some nice bikes

Nishiki - Sweetness

Trek/specialized - good stuff

AVOID

Puegot - French, Smelly and ungrateful.

Sears Bikes in general

This: press fit dropouts


This:Cottered Cranks are super cool but tough to work on and not as reliable.


Almost any old bike that fits you will be usable. For $20 theres not much to lose.

What's with the Peugeot hate?

Yeah, Ok, you may not be able to find parts as easy but they ride nice. An 80's Peugeot will use more standard parts than a 70's Peugeot. Typical 70's and 80's Japanese bikes seem dead by comparison.

Just stay away from the ones with plastic Simplex derailleurs and you should be alright.

I'm never quite sure what exactly the French should be grateful for.

We stood on the sidelines as the Germans ran over them, -not that it took that long. It took us years to decide to do anything about it and I don't think we really did it just to help them out.

Let's see, 1939: France Attacked
1944: D-Day, - We show up

Why they're not proclaiming their undying gratitude on a daily basis is beyond me.

@Francophiles

Yeah but they are like the kid the keeps taunting the bully and then when the bully starts pounding on them you're not sure you want to rescue them. After awhile though it gets to be too much and then you go rescue them. The cheese eating surrender monkeys.

From "American Dad"
Francine Smith: How's everyone's French toast?
Stanley Smith: Smelly and ungrateful! But this American toast is delicious!