I've found whenever I get stuck on something hard, notebooks help. There is something about writing stuff down in a notebook that really helps me think.
Whiteboards are fun and all, but I think they are a little more distracting than useful when you're working by yourself. All of the setup required to just put your thoughts down is a bit much most of the time. Once you're done at the whiteboard, then you have to figure out a way to save your thoughts so you can reference them later. Don't get me wrong, great when brainstorming in a group, but I've found they are way less productive than a notebook when working a lone.
My favorite notebook is the Behance Dot Grid Book (only $14). It's super high quality. I'm a big fan. (I also really like Moleskin too.) The Pilot G2 Pen is my all time favorite pen. I've used it exclusively (when possible) since 2007.
It's really great to flip through past notebooks and see cool things I designed or problems I struggled through that were once really hard that are now easy. Most of my doodles are abstract drawings, UI wireframes, or lists of elements of a problem. I've found I get to a solution fastest by simply listing all of the parts of the problem. It also really helps to simply list (in sentences even) what I will do to solve it.
For some reason, this is so much more effective to me than opening TextMate and doing the same thing. Anyway, I recommend trying this. It has helped me countless times over the years.