Couldn't find any recent info on which dungeons drop decent skill shard amounts.
A couple weeks ago I was getting tons of them, but I think that was from an event dungeon, probably the Bounty Hunter one.
Working my way though Gauntlet and would really like to pump up some of my lesser used toon.
At one point I thought I had a lot of skill shards, but at around 25 per Eddie they go pretty quick.