the following has helped me free up space so now i have about 200 open in my house:
stacking items
throwing away most redundant copies of the new SA quest books
unraveling
salvaging all redundant copies of the old invasion armors.
I have been training my thief by sending him into the dungeons and stealing arties. In my house I already have about 450 arties ready for turn in. I hate to just toss them because I know that as soon as I do, they will announce a cleaining event that i could use these for....