I like what valleycat1 recommended; perhaps position your bed so that is length way against the window? That way you don't loose too much wall real estate on the bigger wall- plus, it is a lot of fun to position pillow against the foot of the bed and have the windows to gaze out of. You could then position the entertainment system in the right corner and make it diagonal so both you and your sister can see the tv while laying in bed. I don't know the dimensions of your room, perhaps the length of the walls would help us help you more!
I can tell you a college trick that your parents might like instead of buying new stuff. We took the bunk beds and arranged to stack each bed high up so each would be on top and then each of us had a work space underneath. Be sure the beds are well anchored. You can then use sheets or drapes or dividers to give each of you a little privacy. It doubles the space of your room and doubles your personal space.
I have an odd shaped room and it isn't huge but isn't tiny... I am 15 years old and share it with my 9 year old sister and I am sick of the bunk beds! so I need ideas on what furniture to get and where to put it... I made a drawing of my room and the stuff that cant be moved (windows, closet, ect.) so I need specific furniture ideas and where to put it try to think of things from ikea
stuff I need:
2 beds (one full size and other twin)
tv (I have a 32 in flat screen that can go on the wall or on a stand but would need something to put it on if not on wall)
nightstand (either one larger table kind or 2 small ones)
I have a malm vanity