hi! there's always room for more input, but meanwhile, here are a pile of previous posts to get you started
Various
How were various countries able to stay neutral during WWII? - many countries
What pressure was put on the non-combatant nations of Europe during WW II (e.g. on Switzerland to allow the Allies to transit into Germany or on Ireland to provide help in the Battle of the Atlantic)? [revised and reposted] - Sweden, Switzerland, Turkey, Ireland, Spain
Ireland
Sweden and Switzerland (often paired in questions)
What was Sweden's role in WWII? - Sweden
How was it that Sweden managed to stay neutral during WW2? - Sweden
What was life like in the Swedish city of Malmo during World War 2? - Sweden
How much did Sweden as a neutral, iron ore rich country profit from world war 2? - Sweden
What was the relationship like between Germany and the various neutral powers of Europe during WWII? - Sweden, Switzerland
What happened in Neutral European countries such as Switzerland and Sweden during WWI and WWII? - Sweden, Switzerland
How did Sweden and Switzerland avoid occupation during WW2? - Sweden, Switzerland
What prevented the Axis Powers from invading Switzerland during World War 2? - Switzerland
Spain and Portugal
How did Fascist Spain stay absolutely neutral during WWII? - Spain
How come nationalist Spain never joined the axis during WWII? - Spain
Why did Spain stay neutral through both of the world wars? - Spain
What was Spain doing i WWII? - Spain
Why didn't Spain and Portugal participate in WW1 & WW2? - Spain, Portugal
Vatican City
Iceland and Faroe Islands