My husband got me the compact edition of the new first edition bilingual, Hebrew-English Koren Siddur. I should really be italicizing "compact" and putting it in quotation marks.
This Siddur (Jewish Prayer Book) is not a light-weight. It's a very complete Siddur. If you only want one, that's it. Though unless I missed it, it does not include T'hillim, Psalms. Another thing it doesn't have, which is hard to find nowadays, is the T'filat HaDerech, Travelers Prayer for Air Travel.
I haven't yet dovened from it, but it seems that the font is easier for my reading-challenged eyes than the Art Scroll's equivalent siddur.
Koren also went against tradition and printed the Hebrew on the left and English on the right, so it will take a bit to get used to. I'm looking forward to a future bilingual version of its popular Shabbat Chumash (Bible) and Siddur combination, and after that I hope that they do a bilingual T'hilim, Psalms.