Paint your concrete foundation for the cheapest, easiest improvement. Many companies make paint or epoxy especially for concrete, in a number of colors. Special waterproofing paint is available, but color choices will be more limited. The only preparation required for paint or epoxy is to make sure the wall is clean and dry, and any cracks are filled with mortar. Epoxy comes in two parts which must be mixed in a separate container before use. Apply paint or epoxy with foam brushes or rollers which can be thrown away after use. If you are artistic, paint colorful flowers or animals on the painted foundation.
Face your concrete foundation with brick or stone. This will depend largely on the walls of the house -- don't use facing that clashes with the existing house. You can use full brick or buy special half-brick facing which is easier to apply. You also can get stone facing in smaller slabs. For a short foundation, lay the brick or stone facing on a base of concrete or mortar the width and depth of the facing. For a taller foundation, dig a footing and fill it with concrete, then let it set for a few days before adding facing. Apply either brick or stone with mortar and a trowel, starting at the bottom and working up. Be sure brick courses are level and match the house siding.
Use a vinyl lattice, sold at most building supply stores. It can be cut easily and can be applied to the foundation with construction cement. There are other vinyl panel options, but colors in all vinyl may be limited.