Excel
Excel Easy - 100's of Excel tutorials from beginner to advanced.
Learn Excel by yourself is a list of Excel tutorials, tips and resources based on different learning methods.
Contextures - Debra Dalgleish has a huge range of tutorials including loads on PivotTables.
Excel Ribbon Tips - Allen Wyatt also has tips for earlier versions of Excel at his a ExcelTips site.
ExcelExplained.com helps beginner and intermediate users improve their Excel skills, using short and easy to follow tutorials
Atlas - Excel MVP, Tom Urtis, is an Excel consultant, trainer and blogger. He also offers an innovative Excel Aptitude Test (XAT®), that enables employers and individuals to measure the Excel knowledge of their candidates and employees.
Microsoft Excel - The Mothership.
Charting and Dashboards
Peltier Technical Services, Inc. - If there's a chart for it you'll find an example on Jon Peltier's site.
Free chart element alignment tool a must have for anyone who works with charts. No more fiddling with chart titles, legends, labels and more. This tool aligns them at the click of a button.
HelpMeViz - Get help with data visualisation ideas and feedback.
Clearly and Simply - Advanced charting for Excel and Tableau.
Principal Analytics Prep - Data analytics bootcamp by Kaiser Fung.
Excel for Educators - Data visualisation opinions and tips.
Templates and Utilities
Spreadsheet123 - Free templates for Excel, Google Sheets and Open Office.
Vertex42 - Loads of free high quality Excel templates.
ASAP Utilities for Excel - The best utility for saving time in Excel.
FinModelsLab - Templates for everything you can imagine.
Code
Repository of code used on this site: VBA, Python, JavaScript
Non-English Excel Sites
Herber.de - Excel and VBA formula, teaching, programming and solutions in German.