No one else seems to want to reply to this one so I figure I'll get it started so 35 people can jump all over me and tell me I'm wrong (and that way you'll get your answer).
So you've got light, stiff, and square; pick two. It's really hard to get a light square BB that's also stiff. The best way to get light is to go Titanium, and that is inherently not as stiff. There used to be some good ones - the Syncros Double Row Ti, for example - but these days everyone is putting their development dollars into splined BBs. Which are light and stiff. I've got an old Syncros Double Row Chromoly which is incredibly stiff, but light is not a word I would use (and impossible to find these days). The Shimano stuff is still readily available and fairly stiff, but is heavy enough to anchor a cruise ship. Everyone else, like Race Face and Truvativ and those guys, either doesn't make a square taper anymore or makes only a heavy, cheap low-end one. Even Ritchey went splined, (Ritchey! Let's observe a moment of silence).
The only nice square taper I can find is Phil Wood, and it's like $200 - for that price you could get a new crank and splined bottom bracket.
Thanks for jumping in. I was worried that the Phil Wood would be real expensive. I am going to check American Classic. Also how heavy is a Shimano UN-73? I may look at this as an option if it is not too heavy.
SKF had some out there. I have not been in the market recently, but it would be one of the first ones I would look at. Check with Larry for the BAS series. Would be one of the following: BAS 300/450/600 ($60/$90/$130 or so approx pricepoint).
Race Face Taperloc. Cromo Versions are about 220g. Increasingly harder to find.
Interloc - just re-released a good version of a Steel square bb. Should be reasonable too. $28 / $40
Phil Wood. He's got a few variations to meet the price and weight that you want. Well, if you want to pay a bit more.
And finally Shimano UN-73. About 250g. Pretty cheap, quality isn't quite as good as it used to be (more plastic).
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