How about Hadoop? Sure Google released the Map/Reduce paper, but it was Yahoo who wrote 90+% of the current industry standard.
What about Node.js? That's pretty en vogue right now. We are currently hiring Node.js engineers and have a number of core contributors in various parts of the company.
YUI and our other front-end work at Yahoo! is world class. People like Crockford are considered leading experts in doing quality front-end web engineering.
Our data centers are also cutting edge, I'm not an expert in this area, but I'm told we are at least on par with Google. Some of the new project are completely cooler-free, the whole building being designed to control heat and power flow.