SQL Developer 4 EA2 includes a performance node in the DBA tree.
You can use this to view ADDM, AWR and ASH reports directly from SQL Developer. I know I can get these from Cloud Control, but previously I tended to pull these out from the command line on the server. This is a much better approach IMHO.
I found out about this stuff at OOW2013, whilst talking to Jeff Smith and Barry McGillin in the demo grounds. I tweeted some pictures at the time, but figured it was worth a post for those that don’t do Twitter.
PS. Yes, it is only going to be of use to people connecting to Enterprise Edition databases with the Diagnostics & Tuning Pack.