Hi!

well, in my opinion, one of the most versatile and best lenses is the Pentax-M 50mm 1.7. Some say it is even better than the 1.4, also it is much, much cheaper. For landscapes i also reccomend the 28mm 2.8 which is also cheap as chips. Unfortunately i can not reccomend anything for macro work since i'm not doing any of that. Portrait neither but most people get a 85mm oder 100mm or 105mm.
cheers