Have you considered calling in a local closet planning company for a quote and design?

Keep in mind that any hanging space requires 24" of depth, (that's about how deep you need to comfortably hang an article of clothing without squashing it up against a back wall, though you can take that down to about 22" deep if absolutely necessary, just not for big coats!)

So if you have hanging on both sides of your long skinny closet, you will have a 24" wide path down the middle of the space.
Make sure if you plan built-ins, that they remain open (no doors), otherwise you'll have extremely tight quarters for getting at your clothes every day!

Consider having hanging on the lower half of the walls, with shallow shelves for shoes and handbags above. This will give you more `breathing`room at eye level, and will make the space feel less cramped.
Alternatively, if one side has hanging, then I would do the opposite sides as 14`deep shelves and/or drawers
This is a space I just completed, which was approx 25 feet long, and 8 feet wide. Imagine making this just 6 feet wide, with no window seat, but rather, more built-ins across, and you'll see how it could be a problem...

http://www.houzz.com/projects/43994/Beaconsfield-Master-Bedroom

Hi Marie, have you started doing any searches for closet photos to see if there is an arrangement you like?

Thank you Joanne and Emily! Yes, I've amassed quite the closet lookbook here on houzz! I have been searching out photos of long skinny walk-ins and getting ideas. I have the ability to include a small window on the exterior wall side of the closet (the renovation/addition has not begun yet). This is something I think I might do just to help me not feel squished in there. I like the idea of shelves above hanging areas to free up the eye-level space, thanks Joanne! I was thinking of acrylic boxes all around the top of the closet to house handbags and shoes/items I may not use on a regular basis (or seasonal ones that I may switch out from time to time) so I can still see them, but they won't collect dust. In my current closet the shoe shelves are open and the dust drives me crazy! Thank you both for your suggestions, I will update from time to time during the 9 month build and add pictures when it's done. Marie

Here are a couple of images from a job we did back in 2007.....each photo shows opposite sides of the same closet. There was about 30" in between the opposite walls (see the mirror at the end? You see it in both shots, showing the two sides of the closet)

Hi marie, do you have pictures of your finished closet? i am trying to design one that will be the same dimensions and would love to see what you ended up with!

I am also looking for the same dimensions and would love to see. :)