There are basic lands for each of the five colors: White is Plain, Blue is Island, Black is Swamp, and Green is Forest.
There are dual lands that are actually colorless. In this case Terramorphic Expanse can be used to add a basic land in any of the five colors. This ability is often found on common dual lands and comes in handy in a multicolor deck that is lacking mana to cast for one of its colors.
There are also other dual lands, typically rares that have additional abilities triggered by specific colors. Alchemist's Refuge does not yield specific types of mana, but it does allow you to add the flash ability during gameplay. The circular arrow ahead of the Green-Blue symbols means that you have to tap this card to activate this ability.
Kessig Wolf Run also has a special function. In this case the X in front of the Red-Green means the extra number of lands tapped in addition to one for each of these two colors.
There are also dual lands that can be used as one of two colors. Drowned Catacomb can be used as an Island or a Swamp.
The Shards of Alara block was based on the concept of three harmonized colors, and to balance the mana for gameplay the panorama dual lands must have been handy. Bant Panorama must be sacrificed to activate its color balance ability. It is a common, and by how cheap a playset was I am guessing it did not rise to the level of a tournament staple.
I have played Reliquary Tower online and have yet to use its ability of no maximum hand size.
