Errors in writing that involve sound-alike words (homophones) are known as "wrong word" errors. Such errors are more significant than simple spelling mistakes, because they involve word-level confusion, not merely incorrect spelling.
This handout contains a list of the most common.

Words that Sound Alike Practice
Spelling: Accept/Except and Affect/Effect
Two common sources of wrong word errors are the homophone pairs accept/except and affect/effect.
This piece explains the difference with plenty of examples.

Accept or Except Practice

Notorious Confusables Part I
Professor Darling has complied 257 examples of words that are misused or misspelled. He puts the words in a sentence. Passing your mouse over a highlighted word causes its definition to appear in the status-line at the bottom your browser window.
Part I covers abhorrent/aberrant to indeterminate/indeterminable.

Notorious Confusables Part II
Part II covers the words from indite/indict to your/you're.

Notorious Confusables: An Alphabetized List
Use this pull down menu to go directly to the confusable of
your choice.

Notorious Confusables Exercises
Notorious Confusables Exercise 1

Notorious Confusables Exercise 2

Notorious Confusables Exercise 3

Notorious Confusables Exercise 4

Notorious Confusables Exercise 5

Its/It's and Their/There/They're

To Lie/To Lay and To Sit/To Set

Resources

Usage & Grammar

Subject-Verb Agreement

Pronoun References

Apostrophes

Commas

Colons & Semi-Colons

Spelling

Common Words that Sound Alike

Capitalization