Here's a selection of foliage that i put together. The first two pieces were simple foam lumps with twigs glued in to look like broken trees. The bushes are little plastic ones brought from a craft shop.
These are from the GW range. Relatively simple to base and paint they are versatile and being based handy to place anywhere.
These were the easiest to make. They are fish tank plants that come in large mats. I just clipped off enough to fit on a 40mm base, added some sand, paint and then water effect to give a swamp effect. Being based they are handy and can give areas of swamp foliage quite easily.