you can buy things that go on top of the shelves in your cupboards so you get extra shelf space, or the little drawers that clip to the underside of the shelves so make a bit more room.
Make sure you keep the kitchen colour light as a dark colour will make it feel smaller. If you have any wall space, hang a mirror or collection of smaller ones to give the illusion of more space.
As a cheaper alternative to new kitchen doors, why not try covering them with fablon? im sure it'd be a lot cheaper than new doors and its available in a load of designs form b&q and places like that.
If you can get a light fitting that doesnt come form the ceiling much - eg spotlights - it'll make the room seem higher.
Hope that helps? x