The June 2008 Good Housekeeping has a great idea for the area under your kitchen sink: add self-stick vinyl tiles to the bottom on your sink cabinet. This will protect it from the spills and mess that inevitable happen there. I'm pretty sure we still have some plain black tiles leftover from the previous owners and I think I may try this.
Among the other good ideas from the article:
• Install a pullout basket for storing cleaners, dishwashing detergents, etc.
• Attach a wire basket to the inside of the cabinet door for sponges.
• Use a riser shelf (normally used in upper cabinets) to expand the vertical space (tuck smaller items, like garbage bag boxes, underneath and put taller items, like a bucket, on top).
• Add a lazy susan in the front of the cabinet for frequently used items.