Let me be the first to admit (after my wife) that I spend too much time optimizing my to do-lists and calendar implementations - more than I actually earn from the process. Like a large number of other like-minded, I am trying to find the perfect balance between easy note-taking and a manageable and computerized system.
I love the immediate availability of a pen and paper in my pocket, although I have been through a lot of other systems like a larger Filofax system (not mobile enough), Palm and PocketPC (too slow compared to handwriting) as well as the cool index-card based Hipster PDA (too difficult to sync with the PC).
GTD is obviously the system of choice these days, with a splash of Covey's Weekly Reviews and role-based goals thrown in for good measures. An eruption of online GTD implementations have become available lately but it's not until now that we are finally starting to see them mature into useful tools.
My vote goes to Toodledo - it has a nice AJAXy interface with GTD contexts, projects, priorities and deadlines. You are able to export your to do lists as RSS feeds, iCAL, and (drumroll...) as a PDF booklet. The PDF export is the feature which really makes it usable for me, and makes me happy to switch from my current Hipster PDA implementation. Basically, it allows you to print out your to do lists to an A4 page which you cut & fold into A7 size, fitting nicely into even the smallest pockets.
I also found out that the classy notebook Moleskine is finally available in Israel. I bought mine from Soho in Dizengoff Center, Tel Aviv.