This page needs to be better organized in some way, maybe by organizing the grammar resources by error? Or maybe having categories for grammar sites and other materials? Any ideas are welcome...

20 Common Surface Errors in Writing

#1 Run on sentence
#2 Sentence fragment
#3 Subject verb agreement
#4 Possessive apostrophe error
#5 Missing comma with introductory element
#6 Incorrect punctuation of titles and dialogue
#7 Unnecessary shift in person
#8 Missing comma in compound sentence
#9 Pronoun agreement error
#10 Homonym error
#11 Incorrect comma with essential & non essential element
#12 Wrong pronoun
#13 Wrong tense or verb form
#14 Comma error
#15 Misplaced or dangling modifier
#16 Tense shift
#17 Vague pronoun reference
#18 Words frequently confused
#19 Faulty parallel structure
#20 Weak passive voice

The following online grammar quizzes and resources will help you practice errors from the List of 20 Common Writing errors.
Review the use of commas in several different situations
#1 - Run-on sentences
#2 - Sentence fragments
#3 - Subject verb agreement quiz
#3 - Subject verb agreement quiz
#4 - Possessive apostrophe error
#5 - Commas with introductory elements
Commas with introductory elements
Another quiz on commas in introductory elements
#6 - Quotation marks quiz
#8 - Commas with two independent clauses
Review the use of commas in several different situations
#9 - Pronoun and other agreement problems quiz
#9 - Another pronoun agreement quiz
#9 - Quiz on pronoun agreement forms
#10 - Homonym error - their/there/they're
#10 - Another Homonym error - their/there/they're
Review guidelines for essential and non-essential elements
#11 - Essential and non-essential elements quiz #1
#11 - Essential and non-essential elements quiz #2
#11 - Essential and non-essential elements quiz #3
#12 - Wrong pronoun
#15 - Misplaced or dangling modifier
#16 - Shift in tense
#19 - Faulty parallel structure
#19 - Another faulty parallel structure quiz

The following are general quizzes to assess general knowledge of grammar and mechanics.
Sentence combining skills #1
Sentence combining skills #2
Sentence combining skills #3
Identifying independent clauses

Here is another site with a list of online quizzes, some of which align with our 20 common errors
http://www.cityu.edu.hk/elc/iowa/quiz/

The writing center at Kent State have a series of Word document handouts dealing with grammatical issues and writing
http://dept.kent.edu/english/WritingCent/lessons.html

Purdue's Online writing lab is quite extensive and contains many mini lessons and quizzes
http://owl.english.purdue.edu/handouts/grammar/index.html

Here is a site dealing with participial phrases: http://grammar.uoregon.edu/phrases/participialP.html and this could be a practice sheet to go along with it: http://www.phschool.com/atschool/writing_grammar/gold/grammar_practice_activities/pdf/09GE2109.pdf

Try these sites as well:
http://ccc.commnet.edu/grammar.com
http://grammar-monster.com/
http://www.lessontutor.com/
http://webnz.co.nz/checkers/grammar2.html
http://xnet.rcc.mb.ca/leshanson/Writing-Resources.htm
http://englishplus.com/grammar/
http://andromeda.rutgers.edu/~jlynch/Writing/