Here's an incomplete list of titles to which the 20% Funimation discount applies. I know for sure some of these are nowhere near historic lows. I'm not going to check each one to put it in here, but if you have any questions about a specific one, ask and I'll try to get back to you.
18 pages of listings. My eyes hurt.
A Certain Scientific Railgun S Season 2 Blu-ray/DVD(42.99 pre-discount)
Afro Samurai: Resurrection Director's Cut
Attack on Titan Season 1 Parts 1, 2
Attack on Titan Complete Season 1 Blu-ray/DVD($36.96 pre-discount)
Attack on Titan Season 2 Blu-ray/DVD($26.79 pre-discount)
Basilisk Complete Series Blu-ray/DVD
Black Butler Season 2 Blu-ray/DVD($32.46 pre-discount)
Black Butler: Book of Murder OVAs Blu-ray/DVD($24.79 pre-discount)
Cat Planet Cuties Blu-ray/DVD S.A.V.E Edition(14.99 pre-discount)
Code Geass: Lelouch of Rebellion Season One
Cowboy Bebop Complete Series Blu-ray/DVD($28.49 pre-discount)
Deadman Wonderland Blu-ray/DVD($19.96 pre-discount)
Death Note Complete Series Blu-ray($27.56 pre-discount)
Eureka Seven Complete Series Blu-ray($45.79 pre-discount)
FLCL Complete Series Blu-ray($24.44 pre-discount)
Fairy Tail Collections 1, 3, 4, 9, 11, and Zero. The collections between 1 and 9 might be on sale. Didn't check individually.
Freezing Season 1 Blu-ray/DVD($22.13 pre-discount)
Fruits Basket Complete Series Blu-ray($43.42 pre-discount)
Full Metal Panic: Fumoffu Blu-ray/DVD($17.99 pre-discount)
Ghost in the Shell Arise: Borders 1 & 2
Hellsing Ultimate: Volumes 1-4 Blu-ray/DVD($29.96 pre-discount)
High School DxD New: The Series Blu-ray/DVD($43.06 pre-discount)
High School DxD Born Season 3
Lord Marksman and Vanadis Blu-ray/DVD($37.39 pre-discount)
My Hero Academia Season 1 Blu-ray/DVD($42.99 pre-discount)
My Hero Academia Season 2 Part 1 Blu-ray/DVD($50.31 pre-discount)
One Punch Man
Ouran High School Host Club Blu-ray/DVD($30.72 pre-discount)
RWBY Volumes 3, 4
Serial Experiments: Lain Complete Series Blu-ray/DVD($22.99 pre-discount)
Shakugan no Shana Season 2 S.A.V.E Edition
Soul Eater Complete Series Blu-ray/DVD($29.96 pre-discount)
Speed Racer Complete Series Blu-ray($19.96 pre-discount)
Steins;gate Complete Series Blu-ray/DVD($24.22 pre-discount)
Tenchi Muyo: OVA Series
Devil May Cry Complete Series S.A.V.E. Edition
The Melancholy of Haruhi Suzumiya Seasons 1 +2 Blu-ray($40.00 pre-discount)
Tokyo Ghoul Complete Series Blu-ray/DVD($42.99 pre-discount)
Yu Yu Hakusho Seasons 2, 3
Only Yesterday Blu-ray/DVD($19.96 pre-discount)
Pom Poko Blu-ray/DVD($15.96 pre-discount)
Tales from Earthsea Blu-ray/DVD($14.99 pre-discount)
The Red Turtle Blu-ray($15.49 pre-discount)
When Marnie Was There Blu-ray/DVD($15.99 pre-discount)
Digimon Adventure Tri.: Confession
Dragon Ball Z Seasons 4, 6, 8
Dragon Ball Z Kai Seasons 1, 2, 3, 4
Dragon Ball Z Kai: The Final Chapters Parts 1, 2
Dragon Ball Z: Android 13/Bojack Unbound
Dragon Ball Z: Fusion Reborn/Wrath of the Dragon
Dragon Ball Z Double Feature: Tree of Might/Lord Slug
Dragon Ball Z: Broly Triple Feature($21.49 pre-discount)
Dragon Ball Z Double Feature: The History of Trunks/Bardock Blu-ray($21.49 pre-discount)
Inuyasha The Movie The Complete Collection
Naruto the Movie: The Last Blu-ray/DVD($14.99 pre-discount)
Pokemon: The Movies 1-3 Steelbook Collection($19.99 pre-discount)
Amazon link for full series on Blu-ray/DVD