This is my best attempt at putting together a bunch of lists of who has filed what for which cause. I may be missing some things or have a few things wrong, so feel free to correct me. But it was driving me crazy having to piece together the whole picture from a bunch of posts, tweets, and articles. So here's the rundown:

Plaintiff / Supporting States

1. Texas
2. Missouri*
3. Arkansas*
4. Louisiana*
5. Mississippi*
6. South Carolina*
7. Utah*
8. Alabama
9. Florida
10. Indiana
11. Kansas
12. Montana
13. Nebraska
14. North Dakota
15. Oklahoma
16. South Dakota
17. Tennessee
18. West Virginia
19. Arizona
20. Alaska

(* = Intervening States)

Intervening Parties

1. Donald J. Trump
2. Michigan State Legislators
3. PA State Legislators
4. PA Voters
5. Dr. Linda Lee Tarver
6. Amistad Project / Thomas More Society

Supporting Parties / Amici Curiae:

1. Constitutional Attorneys
2. PA General Assembly
3. PA State Senators
4. Christian Family Coalition
5. PA Speaker and Majority Leader
6. 126 U.S. House Reps***
7. Arizona State Legislators
8. Idaho State Legislators
9. Idaho Lt. Governor
10. Freedom Fund
11. GA State Legislators
12. Lin Wood
13. Citizens United Foundation
14. New California State
15. New Nevada State

States on the fence:

1. Idaho
2. Iowa
3. Kentucky
4. New Hampshire
5. Ohio
6. Wyoming

Territories on the fence:

1. Puerto Rico
2. American Samoa
3. The Northern Mariana Islands

Defendant States:

1. Georgia
2. Wisconsin
3. Michigan
4. Pennsylvania

States Supporting GWMP**:

1. California
2. Colorado
3. Connecticut
4. Delaware
5. Hawaii
6. Illinois
7. Maine
8. Maryland
9. Massachusetts
10. Minnesota
11. Nevada
12. New Jersey
13. New Mexico
14. New York
15. North Carolina
16. Oregon
17. Rhode Island
18. Vermont
19. Virginia
20. Washington

Territories Supporting GWMP:

1. Guam
2. U.S. Virgin Islands
3. Washington DC

Other Parties Supporting GWMP:

1. Montana Governor
2. Detroit
3. China
4. FBI
5. MSM
6. Silicon Valley

**GWMP = Georgia Wisconsin Michigan Pennsylvania

***Update: 20 other U.S. House Representatives have joined Rep Mike Johnson's Amicus Brief. Keep up the good work everyone! https://www.supremecourt.gov/DocketPDF/22/22O155/163550/20201211132250339_Texas%20v.%20Pennsylvania%20Amicus%20Brief%20of%20126%20Representatives%20--%20corrected.pdf