Can you do physical? I have found that carrying a pen, and a packet of sticky notes in my pocket at all times is the way to go. when I get home, Ill peel off the sticky, and organize it. I do it a little different though and organize things by "backlog", "Today", "tomorrow", "this weekend", "hold", because I find it suits the way I work as an individual (ie, I save stuff like washing the car for the weekend etc)
I've only played around with it for a few minutes, but it seems feature rich with a free account option. See <a href="http://kanbanize.com/" rel="nofollow">http://kanbanize.com/</a>