[Jtsummers]

Check out Staples line of Arc products. Similar to a spiral notebook in how you can fold it, but the sheets come out easily like a 3-ringed binder and can be reordered. The first page in mine is blank. I write the date and topic at the top, use as many sheets as I need. Then move them to the appropriate section or into another Circa notebook (as appropriate). The covers and disks to create more notebooks are reasonably inexpensive, and you can purchase your own punch for a modest price to make compatible paper out of any paper stock you have available (and to make printouts and such fit into it easily).

Levenger's Circa line was my introduction to the concept, but their notebooks and paper are more expensive and less available (compared to having a Staples in nearly every city).

I use the Junior sized notebooks (8.5"x5.5", or roughly A5 sized for those not in the US). It's not a pocket notebook, but easily carried and fits nicely into most bags. Being able to reorganize the pages also reduces, for me, the difficulty of first writing something down ("crap, it doesn't need to be in this notebook!" kind of nonsense).