Ok, well I really don't have the solution for that. If I did, I suppose I could bottle it and make a ton of money! As I have been working today on a bunch of clients sites and tasks, I was thinking of something that I do (in regards to time management) that really makes working on multiple projects/tasks much easier on a day to day basis.
Proper time management plan - you can break down (on a whiteboard above your computer monitor) your series of duties on a daily basis. On Monday I need to accomplish A, B and C for client A, B and C, and so on for each day of the week you plan on working. You can break this down into days, and even how many hours you are willing to spend on each task.
If you are needing help with time management for marketing a site, you can use the same method, just break it down with marketing tasks/day; How much time will be spend on blogging, finding links, writing content etc. ... and whatever the tasks are. If you get into this habit you will no longer be overwhelmed, and will accomplish more then you ever thought possible!
But I am serious about the white board. Go to Office Depot today and buy one. Stick it up in your office right in front of you. Lay out your day to day tasks as I have suggested and you will be surprised how much more productive you will be.