The Aesir of the Norse
The Norse worship the Aesir and Vanir, as they have since the oldest of days. While their civilisation is considered by many to be barbaric, they have lived in the mysterious wastes of Nordmaar since the earliest of days, and their gods are counted amongst the oldest, being worshipped long before St. Cuthbert brought the Holy Trinity to Leng.
The origin of the Norse gods is not clear; however, due to their close association with light, fire, life and the earth, as well as their age-old connections to the realms of "Alfheim and Svartalfheim" (referring to the Seelie and Unseelie courts of the Fae), it is believed that they are closely tied with the Realm of Fae. This is supported by the fact that Ysgard borders on the Fae in many places, and that many of the Nine Worlds exist at least partially in the realm of Fae.
In addition to the Aesir and Vanir, there are many significant beings to the Norse Mythos - powerful "alfar" or "svartalfar" and other beings such as Fenris, Surt, Fafnir and Nidhogg, as well as specific entities such as the Norns. Although many of these are part of their legends, the Norse are not prone to worship or ask for the aid of the gods, at most calling on Odin or Thor for courage, or Frigg for fertility. Instead, Norse priests make use of Odin's great gift to the world; the runes, which hold individual power, and which they use to call upon the power of rune-magic, which they know as Galdur.
Because the Aesir and the Vanir are on the order of divine heroes rather than deities that take followers and grant powers, worshipers of the Norse Pantheon do not generally gain piety - their gods have little interest in them. Worship of the Norse gods has few direct benefits, and few Norsemen actually worship them as such. The Aesir and Vanir are venerated, viewed with respect, and treated alternately as both ideal to live up to and cautionary tale, depending on the particular story being told.