The ACM digital library has a new portal (currently in beta). They've also strengthened their search engine, added author profile pages and will start indexing best paper and other award winners. The digital library interfaces well with Google Scholar and other search engines and indexes many non-ACM publications (Tip: To get to a non-ACM publication page from the digital library listing click on the DOI). ACM continues to impress on its DL when I find so many of the others lacking in functionality or ease of use.
I'd also like to mention a little known service, the ACM International Conference Proceeding Series (AICPS). For conferences, mostly foreign, who don't want or need ACM sponsorship, this series gives them the opportunity to have their proceedings in the ACM digital library, a good alternative to the Springer LNCS series. In theory the CATS conference (Australia area theory) uses AICPS and I wouldn't mind seeing many other theory conferences heading that way.