Lighting-The fixture or even just the bulb. Soft and pretty light can transform a space. Replacing or refinishing a fixture can transform the very style of a space.
Hardware-Cabinet pulls, door knobs & such. Replacing or adding cabinet pulls changes the entire function and look for a very small price.
Accents-Toss pillows, rugs, lamp shades & such. Taking down dated or disproportioned accents and adding those better sized for a space can change a room by tricking the eye to see more space or higher ceilings.
Window Treatments- Sometimes removing and sometimes adding. Something as simple as removing a dated window treatment or adding a simple modern panel can freshen up a room.
Paint-Changes everything. A bad color or sheen can change the way you feel in the space. The way light moves about in a space. A light reflective paint shade with a good undertone for the light in the space can brighten the entire feel.