Fantastic resource, and mentioned here many, many times. Here are some previous submissions:

http://news.ycombinator.com/item?id=1262968

http://news.ycombinator.com/item?id=203317

http://news.ycombinator.com/item?id=86365

You can find many, many references with this search:

http://searchyc.com/projecteuler?sort=by_date