I don't know of any site that provides multiple translations on the same page, but here are all the English Tanach websites that I know of. (Italics means the site only contains the first five books (Pentateuch), and an asterisk means it also contains select portions from Prophets (Haftorah). Regular font means the full Tanakh\Jewish Bible is available):
- Old JPS (1917)
- New JPS (1985)
- Judaica Press (Chabad)
- The Living Torah by Aryeh Kaplan
- The Bible by Isaac Lesser - The first Jewish English translation
Online translations that only allow partial viewing (Via Amazon.com's "See Inside" or Google Books):
- Artscroll Tanach
- Artscroll Chumash* (Same translation as the Tanach)
- Artscroll Chumash* (Alternative Listing)
- The Five Books of Moses by Robert Alter
- The Five Books of Moses by Everett Fox
- Chumash by R' SR Hirsch*
- The Koren Jerusalem Bible
Other translations may be available online, either in full or via Amazon or Google Books. For example, the JPS Study Tanach, which is the New JPS plus additional commentary, is available on Amazon.
I unsucessfully attempted to find the "Birnbaum" translation, which should be out of copyright, but it's apparently not available online.
Differences between translations:
Wikipedia has a list, with distinctions, of many of the major Jewish translations. You can view it here: http://en.wikipedia.org/wiki/Jewish_English_Bible_translations
This website also compares several different translations: http://www.bluethread.com/reviews/chumashim/index.html#Translation
Here's my personal opinion of the different translations, based on an somewhat-extensive unscientific survey:
Old JPS is based primarily on the KJV, but with major changes. It's
pretty literal, accurate, and highly regarded. The main problems are
1. It's based on the KJV, and inherits a few of the KJV's problems; 2. Uses outdated English; 3. Doesn't have any translations based on
linguistic research done since 1917. New JPS vs Artscroll: Both strike
a middle-ground between strict literal and paraphrase, but Artscroll
is more literal than JPS, and the JPS takes some (unjustifiable)
liberties. For example, JPS will re-order the position of entire
phrases (and rarely, verses) to make the English flow better.
Artscroll will re-order words, but never whole verses. JPS breaks up
the English paragraphs according to what they thought made sense,
whereas Artscroll follows the Hebrew paragraph breaks (usually). JPS
breaks up poetry into stanzas, which Artscroll does not do. In
addition, Artscroll is unabashedly Orthodox, whereas JPS is
non-denominational. This has the following implications: 1. The
Introductions to the translations could not possible be more
different. Artscroll has a ultra-Orthodox, "the Bible was never
changed" approach (which is blatantly false, and has been acknowledged
as such by traditional sources), whereas the JPS has a more academic
approach. 2. The JPS has footnotes which frequently acknowledge when
they're not sure of the translation of a certain word of phrase.
Artscroll, following their ideology, almost never admits they don't
know what a word means, and will give the "traditional" interpretation
of that word without indicating such. They also (rarely) bend the text
to match Halakha (Jewish Law) instead of the exact translation.
Finally, Artscroll (depending on the version you buy) includes an
Orthodox\Traditional commentary, which provide "Midrashim" and the
interpretations of Rabbis and the Halakha (Jewish Law) on certain
verses. JPS's commentary (again, depending on version) are more
concerned with the text itself - for example, it'll say when a similar
phrase is found elsewhere.
There are other translations, as well. For example, Artscroll provides
additional versions that are based on a particular Rabbi's commentary.
In addition, Robert Alter has a very good translation of the
Pentateuch and Psalms). Everret Fox also produced a very unique
translation of the Pentateuch, which attempts to keep the Hebrew
syntax. Finally, you should avoid The Living Torah translation, and
any translation by Aryeh Kaplan. Great man, but the translation is
more commentary than text.
A good traditional general-purpose commentary that explains all the
verses and provides short summaries and background information, then I
highly recommend the Hertz Chumash, written by one of the former Chief
Rabbis of England. It's older, and can sound some-what outdated, but
it's still the best general-purpose Chumash around. If you're looking
for a narrower commentary, keep reading. If you're looking for a
strictly traditional (ultraOrthodox) approach, then Artscroll (Stone
Chumash) is the way to go. If you're looking for a more academic
approach, then Robert Alter's translation and commentary is
recommended. If you're looking for a mix of tradition and academic,
then I highly recommed the Da'at Mikra series (Hebrew only). If you're
looking for a more progressive commentary, that's still somewhat
traditional, then I recommend the JPS Study Bible. If you're looking
for a traditional commentary that attempts to connect the verses to
modern life, then R' Samson Rafael Hirsch's commentary is the one.
There are commentaries to fill all niches.
Of course, there are also the Traditional commentaries written by the
Medieval Rabbis, such as Rashi, Ramban (Nachmanides), Ibn Ezra and
Abarbanel, to name a few. Artscroll has published English translations
of Rashi and Ramban, and I believe translations exist for other
commentators as well.