Hi Renton:
Brenton's translation is the only widely available English version of the Septuagint that is around, at least as far as I know. It is not a bad translation, but the language is a little stilted, as so many 19th century translations are. Think about some of the old translations of the Nicene Fathers on CCEL, for example. Still, I think it is worth having in your library.
Having said that, there are some other options on the horizon. There is an Orthodox Study Bible OT that is in the works, and hopefully will be available in the next year or so. There is also a translation of the Psalms done by a monastery near Boston -- I can't remember the name though. Sorry about that.
I may be wrong, but I thought the Douay-Rheims was a translation based on the Vulgate, which has some differences from the Septuagint. Somebody set me straight if I am wrong!
Fr. Dcn. James