If you want cheap solution, but not so nice effects. You can use photoshop the photos to get your effect, but it probably be inferior as compared to better lens and using a polariser.
As for the more expensive solution, you can make use of a circular polariser for bluer sky, but it depends on your angle of shot.
Whereas richness and actual reproduction of colour, you probably have to invest on better lens (as suggested by Leong23, a TS shift lens would be useful) and maybe a wide angle lens (e.g. 10-22mm or a fisheye)would be useful too. However, do factor the effects you want to get with barrel distortion and stuff.
Go with what you can afford ba. Do the best u can with the tools you can get