Where to begin?
~A buttload of makeup
~About half the clothes in my closet.  Either I bought them too small, convinced that the weight I gained will disappear (it's true that it's so much harder to lose weight in your 30's), or I bought stuff on sale that looks terrible.  I return a ton of stuff after I take it home, compare it to what I own and say "nope" - but it appears that I don't return enough.
~My house.  I hate my house.  I should be grateful to own one, yada yada yada.  Yes, I know all that.  Save the guilt trip.  I sold a condo I loved for a house I hate.
~My wedding ring.  Shouldn't have been cheap.  Should have spent an extra $200 for slightly larger stones.  Looks too small next to my engagement ring.
~Many many cds (although I don't own Ace of Base.  But my husband does

 at least it wasn't my money that was wasted)
~Random household stuff and kitchen gear
So much more.  I have the worst case of buyers remorse, yet my house is continually filled with crap.