(download for bigger version)
From left to right: Näcken (nix), trold/troll, lygtemand (light/lamp man), ellepige (elf girl made of mist), nisse/tomte (gnome), dwarf, huldra (a form of elf), slattenpatte (saggy breast,a form of elf/troll), mosekone (bog woman, another form of elf), huldufólk (elf from Iceland).
I love Nordic mythology creatures far more than what's healthy.
When people want to use one of these guys in a story they often ask me which other mythological creatures they usually interact with, and the answer is: all of them. It's pretty popular to draw them all partying together, for example.
When using these creatures it's important to understand that they are considered a people, with each race having their own society, norms and laws (except näcken who is a more solitary creature). So they have every day lives, meet, make friends and fight each other across races.
Also, one thing they all have in common is that if humans treat them right they will be helpful and make friends with the humans, but if humans disrespect them they will take revenge. Some are easier than others to befriend. The nisse/tomte lives on farms and will help the farmer as long as he remembers to feed him and don't tease the nisse/tomte too much. The trolls are pretty easy as well (at least in Denmark and parts of Sweden). The various elfs however are more difficult and humans should only ever interact with them if they know what they're doing, or the elfs will make them go crazy.
And don't forget, they have special power over people who think about sex.