I've got to go with Wayner: Vintage Dynaco's, in my case A35s. Alot of bang for not much bucks. I don't play them very loud though.
some more modern runners up:
Paradigm Atom (haven't heard the newest version)
Magnepan MMGs
by reputation (would like to hear):
Reynaud Twin
Audio Note AX-2
Spendor S20
Gini LS3/5a "clone"
I find it interesting that vintage speakers are mentioned. It is generally agreed that speaker design has made leaps and bounds forward progress over the past 10 years or so. Computer assisted design, tighter manufacturing tolerances, etc. have in general made todays moderate priced speakers perfrom on a par with much more expensive counterparts of yesteryear.
The bang for the buck was not meant to tie it to a given price point. Having said that, there is a law of diminishing return with everything, including speakers. Just trying to get a feel of where that line is.
By the way, DIY are good candidates. I'm reasonably comfortable with the fact that DIY tube amps can give outstanding performance, and provide a return on investment one cannot obtain with Audio Research, Conrad Johnson, McIntosh, etc. (IMHO)
Just a note about vintage speakers, there have always been very good speakers and after enough years many of them have receded from the popular memory. That, my friend, means that there are some bargins out there as many of the younger people won't waste their time with brands they've never heard of.
One brand of speaker that can be a very good bang for the buck are the Braun/ADS speakers. I've got a pair of the ADS 570/2 in walnut veneer cabinets in nearly mint shape, and I picked them up for ...$1.00! The more elaborate models (3-ways, biamped, etc.) were excellent and can better the majority of today's speakers, in fact my more modest 2 way is good enough to shame many vaunted bookshelf speakers.
Another one that's still a good speaker is the AR3a. Refurbished with clean pots and caps they still sound very good and given a decent amp can still deliver pretty good sound. If you build mirror imaged baffles over the existing baffle you can get even better performance. Listen to a pair that's been brought up to specs along with an amp with some horsepower and I think you'll agree that they're not too shabby at all. Best of all they go for very modest prices, my pair were given to me by the original owner.
Older Tannoys, Kefs, Dahlquist and so forth offer the opportunity to get some real great sound and if you're lucky, for very little money. In fact, I turned down a free pair of the big Dahlquists recently, because I just didn't have room for them. These can be modified and mirror imaged for very little and deliver great results.
Lots of good stuff out there and if you're patient you can have a really decent system for peanuts. I once bragged (on another forum) that I had "The World's Best Under $100 System" and was I ever embarrassed, as people such as Dave (Planet 10), cleaned my clock.
I personally like DIY, but I'm not one to pass up a vintage bargin.
Best Regards,
TerryO