+1 for the Nexus 7.
I have the older Wifi 32gb version, rooted and with CyanogenMod installed.
Runs Sky Safari Plus perfectly; I've removed all other astronomy apps because they just don't measure up.
I also have a 10" Asus Transformer TF101G, older Android tablet, rooted and with the Katkiss Mod installed. Also runs Sky Safari perfectly.
The display is bigger of course, but the 10" tablet is a lot heavier, to the extent that I'm probably going to sell it.
I find I use the Nexus 7 for just about everything these days, and can really recommend it!
It doesn't have an extension port for SD cards, but I've got stacks of ebooks, music and pictures on it, no problems with drop outs at all.
Chris