Nice list! But I feel you may have overlooked some other great google web fonts.
For example, Open Sans and Arimo are two good Sans fonts created by the awesome Steve Matteson. I am currently using Arimo for my new project, and it s a nice replacement for the vanilla Arial/Helvetica [Neue].
Oh man, don't use Arimo, or its identical twin Liberation Sans. It is to Arial what Arial is to Helvetica; a metrics-compatible replacement that tries to do its own thing and winds up just awkward. The stupid little serif on J annoys me to no end, and all the capitals look almost like small-caps compared to the lower-case.
By contrast, Open Sans is lovely, go nuts with it. :)
I can't (off the top of my head) think of any Google Web Fonts entries that are quite as bare-bones plain as Arial, but you might want to look at Open Sans (mentioned previously), Lato, PT Sans... maybe Asap, Signika, Cabin. That should be enough to get started with. :)