I considered adding the Cosworth, but didn't really know much about it. As far as European engines, they don't seem to stick with the same engine for too long. Even the Cosworth has seen its age. Almost all of the engines I listed are popular engines to build without a swap, or to swap into other cars. The only exception is the Ecotec, which is a brand new engine, already making a hell of a splash in the performance category.
The 1.8T engine so popular in Volkswagens is undoubtedly well-built, but is oftentimes swapped out, and is rarely built to high standards and high performance, as the other options are.
As far as availability being a factor, you could ask Ferrari to build the greatest 4cylinder engine ever, and if they wanted to, they probably could. There would be 10 of them total and they would cost as much as an F430. Instead, look for an engine that is built to be a reliable motor with power potential, and just happens to be designed so that it makes power without relying on a pure race platform, and all while keeping within the company's design budget.
It takes a hell of a well-built engine to make power on a budget, which is the goal of the engineers that made them in the first place.
That's why the Civic is a great tuner car, why the AE86 is a great track car, etc. Cheap budget, priceless design.
Don't think I'm hating on domestics with this debate, but this is the 4 cylinder design we're talking about. The Japanese have RELIED on a straight-4 layout, and have since come to perfect it better than Americans. Same reason you wouldn't see much competition from Japan in the greatest 8 cylinder engine category, even with the JGTC motors having a stout history.