Hi Meru,
Going along with what Paul said, I too am finding the 10mm (120x) on my 10" dob hits the spot nicely for galaxies (and sometimes the 7mm).
Regarding eyepieces, just throwing in my two cents worth here, drawn from my own experience ...
The first one I'd be buying is a replacement for the 10mm 55deg fov plossl that's sold with a dob telescope. I found it didn't fit many things in it's little fov (large globular clusters amongst them), I would lose objects easily as they travel across the fov, had trouble finding things, and the tight eye relief was the last straw- very uncomfortable for me in every way possible was this little plossl. Since I bought my Pentax XW10mm over 2 years ago, it's been my most used and loved eyepiece. And! It doesn't fog up due to it's weatherproof construction.
