adding to what Jazz said, all lenses can serve as landscape lenses, even short to long telephotos. That said, wide angle lenses have that pop that comes from field of view different from what we normally see with our eyes.
As far as i've understood in the short time i've been in photography, quality=price is pretty much a justified argument (as far as lenses go) so there's compromises to be made, depending on your needs/desires and willingness to part with your money

. However, even kit lenses can produce magnificent results.
While 20mm by Panasonic is known for its price/size/sharpness/quality characteristics, it's one of the lousiest autofocus performers (probably not a big deal in landscape photography) and some copies are more prone to banding on Oly bodies. I'd recommend that lens, but it being a 40mm equivalent, do take into account it lies in the middle of the normal field of view (35-50mm equivalent). Olympus 12mm is a great performer and perfect for landscape photography but it's (unreasonably, IMO) expensive.
as far as zooms go, the ones that Jazz said are best normal zooms currently avaliable. They come with a price tag (and additional weight). UNfortunatelly, our system is not developed in the measure Canon and Nikon is, so after those, you're only left with kit lenses.
Oly 14-42 II and
Panny 14-45. While not necessarily bad, they are producing lower quality results as oppose to primes. They will do for most of your needs, but don't expect superb IQ, sharpness and (naturally) ultra shallow DOF. Additionally, you have
12-50 Oly kit lens (came with E-M5). It is a bit more money, and the quality is still not up to the quality in prime lenses, but you get that 12mm (24mm equiv.) and 50mm (100mm) FOV. Bad side is that it's a bit more $$ than other ones, but the good side is weather sealing (take in mind you don't have a weather sealed body) and faux macro capabilities (at 43mm if i'm not mistaken). I'd recommend the latter.
Have fun and welcome to the forum
EDIT: longer zooms, same thing, more choices (especially on Panasonic side). Not gonna name every single one, but there are options, cheaper and more expensive, lower quality ones and better quality ones. Definitely think if a power zoom (14-150 Oly and 14-140 Panny) would suit your needs more appropriately.
EDIT 2: i forgot two pancake kit zooms, 12-32 Panny and 14-42 EZ Oly. Heaftier price, solid quality.