I keep hearing great things about Getting Things Done. I recently saw a review of it on Slashdot. The key insight is that you pay much more than you think for multitasking and context switching. If you accept that you can only do one thing at a time then you can get a lot more done. If you are already in an interrupt state, do quick things. Then settle down to concentrate to get some specific block done, if you can’t define a block that you can get done in the time you have available restructure. The review summarized his method as 3D. Do it. Delegate it. Delay it. The rest is a system of reminders so that you aren’t maintaining state about stuff you aren’t currently doing in your head. In the comments there was a link to a page summarizing the entire method that I found really useful. If you feel like you are thrashing rather than being productive, check this stuff out.
Dave Allen’s Getting Things Done