Firstly, my sympathies!
As someone else suggested, those CDs really would work so much better as mp3s, and then you could get rid of the stereo too - just use your computer to play music. Or replace it with an Ipod and get one of those tiny speaker sets to go with it. I am all for scanning papers too - I used to be a teacher, and I have boxes of resources that I can't get rid of - a future project for me is to scan everything and make several backup copies. It would be a great habit to get into now, at the beginning of your career - I have so many boxes to get though -- it would be so much easier if I had done it along the way!!
A few ideas:
The shame corner might work as a bookshelf or closet?
Could you rearrange the furniture in the room? Shifting things around might give you a little more space.
I would definately paint those walls a solid, cool colour, to make the space look bigger. A similar idea to make the space look less cluttered, but without really changing much would be to put doors on your shelving. All the different book spines and photos etc are too close to appreciate in such a small space, and just contribute to the closed in feel.
If you really love those pictures you have up there, maybe you could use scans of them as your backgrounds on your computer desktop, or get a plain photo frame and change the picture every month? Just get it big enough to fit the largest one, and make the others fit by placing sheets of card or paper behind them.
Also, how about changing your computer to a lap top? Then you could store it in a hanging messenger bag, and maybe get a smaller desk, or at least have more room on your current desk. Maybe then you could get some document trays or the hutch someone already mentioned.
Under-bed storage would be great for you. If your dad is handy, maybe he could make you a new bed or desk. This desk would be fantastic for a small space:
The free plans are here: http://ana-white.com/2010/02/plans-bedford-secretary-top-insipred-by.html
There are great bed ideas there too: http://ana-white.com/category/plans/plancollections/storage-bed-collection
How about some hanging shelving - like those old fashioned kitchen pot hangers that are on a pulley? If you had a rectangular one you could screw heavy duty cardboard boxes to the top of the rack and store stuff you don't use too often up there. A round one could be used to hang things from.
Do you have access to the attic? I think your real problem here is that you are trying to fit an adult life into one small room. We have so much more in our lives when we are adults - your Mum really should recognise this, and be less greedy with 'her' space. Could you negotiate to take over part of the attic?
I am currently going through a de-cluttering process myself, and it is *so* hard at the beginning, but once you get into it, it really does get easier. I have a hard time throwing anything out, so I donate everything I can. I would start by getting rid of everything you don't currently use or need - think how much fun another kid could have with that jigsaw you love?
Best of luck! Tell us how it turns out!