Athena's Armor Set Search [forums.minegarde.com]
Allows for the search of possible sets for your desired skills.
Requires Download

Armor Skills [monsterhunter.wikia.com]
Armor skills + What they do + How many points you need for each skill

Food Skills [monsterhunter.wikia.com]
Food combinations + Food skills + What they do

MH4U Charm Values (EN) [docs.google.com]
Min-Max values for charms and what talismans they are from.
1st row for a skill indicates the value of skill 1 while the 2nd row of the same skill indicates the value of skill 2.

MH4U Spreedsheet [docs.google.com]
Many spreedsheets for different aspects of the game.
Tablet Friendly

Relic Spreadsheet [docs.google.com]
A spreadsheet of all relics that is easier to look at than the link above.

Jewels [kiranico.com]
All decorations and required materials to make them.

Kinsect Tree Upgrade Paths [imgur.com]
Kinsect paths, their required power/stamina/speed, and skills.

Expeditions + Guild Quests [monsterhunter.wikia.com]
How to unlock certain monsters on expeditions and what guild quests they reward.

Relic Armor Skins [imgur.com]
How all the relic armor pieces look in the game.

Relic Weapon Skins [monsterhunter.wikia.com]
How all the relic weapons looks in the game.

Max Relic Weapon Stats (EN) [www.gamefaqs.com]
Shows the max stats for relic weapons.

Relic Weapon Stats (JP) [wiki.mh4g.org]
More informative than the link above.
Weapon catagories are located at the top of the page where the text is highlighted in pink.

Relic Armor Stats (JP) [wiki.mh4g.org]
Shows the min-max values for relic armors.
The values are straightforward and easy to make out despite the site being in Japanese.