Grammarly
Grammarly Blog: Spelling Words With Ei and Ie
The page focuses on the rules and examples for spelling words with "ei" and "ie" including the "I Before E Except After C" rule and the "I before E, Except after C, unless it sounds like A, as in neighbor or weigh" rule. L.9-10.2c Spelling
Other
Donna Young: Spelling Rules Words With Ie or Ei
Rules and examples for correctly spelling words with ie or ei.
Online Writing Lab at Purdue University
Purdue University Owl: Spelling Ie/ei Rules Exercises
A very good reference for spelling that outlines the rules for EI/IE and the exceptions, and provides exercises for understanding. L.11-12.2b Spelling