If these units are a little too small, but a full size dishwasher is still too large, there's the self standing Danby 18" Portable Dishwasher, which holds 8 place settings, is on wheels for easy storage and is even Energy Star compliant. Looks great to wheel out and then wheel back into a corner or closet when not needed.
EdgeStar model which we like for its silver exterior and stainless steel interior (if black is your preference, a similar Koldfront model is available). At 19.3" x 22.3" x 18.5" and 39 pounds, this portable dishwasher could even be pulled out for special occasions and then put away when not needed. It's too bad we don't even have the space for something this small. The unit has the capacity to fit up to four standard place settings and accepts plates up to 11" in diameter, connects with a faucet adapter, and uses an internal water heater that can heat up water up to 158°F. Reviews on Amazon are mostly positive, though some issues about trouble after a few months are reported, no huge surprise considering the price point.