For dungeons and group play, I recommend taking Bladedancer over Ranger. The ranger talents are very meh in group play (and you won't need the pet), whereas with Bladedancer you can get +5% hit and an extra 50% damage on auto attacks. I also recommend changing up a couple point distributions in the assassin tree. Try this: http://rift.zam.com/en/stc.html?t=0MVMp.VV.0VRfxofodb
I got rid of Improved Final Blow and Improved Savage Strike. They are inferior moves to the Bladedancer versions, and +5% crit chance is much better anyway. I also took the 2 points out of Physical Trauma and put them into Magnify Pain. You can put later points into Physical Trauma (it's certainly good if you'll be using the bleed moves regularly, which you very well may in group play) but I think Magnify Pain is slightly better. I also took points out of Poison Potency and put them into Cruel Vengeance. Increasing poison damage may be good, but I think the extra damage from crits will be much better. Finally, I took Foul Play. A free 4 second stun is incredibly useful, even in dungeons against trash mobs.
Also, for soloing you really should take Blinding Powder in the assassin tree, but since we're talking about dungeons it's not quite as useful.