I was playing with FocusAssist (
http://war.curse.com/downloads/war-addons/details/cowboy-focus.aspx) essentially you click on who you want to assist and run a macro - it stickies the person and then you just use assist as usual. The advantage is that it allows you to have a different person as a defensive target than who you are assisting - so if you have a proc heal for player as part of your attack.
I've been looking at Assist addins and many fall short in one way or another.
I was looking for an addin that:
1) Follow Focus Assist - for setting who to assist & allows you to assist one person and have a defensive target for another.
2) Allows 2ndary assists - so you can set the 2ndary to a squishy and allows quickly switching to them should they take dmg
3) Uses a chat window to pass info around within the group - so all can use the same primary/2ndary assist.
4) Displays a graphic so you know who the primary/2ndary assists are - and displays when they are both taking dmg