Apart from the games you can claim, you need to download them before the sale ends or they will be gone, the ones you can claim will stay in your library forever. Keep checking this Itch.io sales link, because new games keep added every week.

[New]
Crypt Shyfter: Storm Shadow https://itch.io/s/14199/new-crypt-shyfter (with claim, Ends Thursday at 5:00 AM)
Hazel Skies https://itch.io/s/14195/halloween-sale (with claim, Ends Thursday at 5:00 AM)
EPONYMOUS https://itch.io/s/10753/halloween-flash-sale (with claim, Ends Thursday at 10:00 AM)
Petri https://itch.io/s/14184/halloween-1k-x-50k (with claim, ends Friday at 12:00 AM)
No Response https://itch.io/s/14018/no-response-free-for-halloween (with claim, ends Thursday at 3:00 PM)
TOTR (Triumph of the robots) Beta 1 https://itch.io/s/14164/totr-beta-halloween-special (with claim, ends November 9th 2018 at 3:00 PM)
Mio's Fruit Hunt https://itch.io/s/14108/free-period (with claim, ends Friday at 10:00 PM)
Zissi's Island https://itch.io/s/14109/if-anyone-downloads-this-i-will-eat-poo (with claim, ends November 4th 2018 at 5:00 AM)
Amidst Twilight https://itch.io/s/14105/release-sale (with claim, ends Thursday at 7:00 PM)
Don't Get Crushed! https://itch.io/s/13439/giving-out-free-candy-sale (with claim, ends Thursday at 6:00 PM)
Error #54 https://itch.io/s/14092/halloween-sale-d (with claim, ends Friday at 10:00 PM)
Help or Die https://itch.io/s/14028/help-or-die-launch-sale (with claim, ends Thursday at 5:00 PM)
Avner https://soundguy.itch.io/avner (download only, offer ends in 5 days)
Toil and trouble https://itch.io/s/14008/all-hallows-eve-sale (with claim, ends November 1st 2018 at 5:59 AM)
Being One - Episode 6 & Killer Escape 4 https://itch.io/s/13999/halloween-2018-killer-escape-4-being-one-6-free (with claim, ends November 4th 2018 at 10:00 PM)
Echo In The Dark https://itch.io/s/13962/swift-halloween-100-off (with claim, ends November 1st 2018 at 6:00 PM)
Explobers https://itch.io/s/11180/explobers-for-free-explobe-freely (with claim, Ends July 1st 2018 at 6:00 AM)
Evangelion https://itch.io/s/11051/summers-out-sale (with claim, Ends July 31st 2018 at 1:00 AM)
2 Art books https://itch.io/s/11576/get-it-while-its-hot-outside (with claim, June 30th 2018 at 12:00 AM)
Clockwork https://itch.io/s/11674/free-pay-with-a-review (with claim, Ends June 30th 2018 at 7:00 AM)
The Adventures Of The Rectangle https://itch.io/s/12006/the-adventures-of-the-rectangle-10-now-available (with claim, Ends June 20th 2018 at 8:00 PM)
Investi-Gator 2 https://itch.io/s/12156/the-big-savings-sale (with claim, Ends June 27th 2018 at 6:00 AM)
Orbital Brawl [BETA] https://itch.io/s/12252/summer-32play (with claim, Ends August 20th 2018 at 1:33 PM)
Koi Puncher MMXVIII https://itch.io/s/12209/koi-puncher-mmxviii-for-free (with claim, Ends July 31st 2018 at 6:00 AM)
Chris Edward: A Mansão https://itch.io/s/12198/play-for-free (with claim, Ends June 20th 2019 at 4:22 PM)
Love is the Plan, the Plan is Death https://blood-w.itch.io/love-is-the-plan-the-plan-is-death (download only)
CyberShmup https://degtri.itch.io/cybershmup (with claim)
Qbex https://b10k-games.itch.io/qbex (with claim)
Lone Castle (Android Game) https://itch.io/s/11218/castle-sale (no claim, download only, Ends December 31st 2018 at 10:00 PM)
Lone Castle https://rbogames.itch.io/lonecastle (android apk, no claim, download only)
Chimera Crusader: https://manstersoft.itch.io/chimera-crusader (claim, Ends January 1st 2019 at 5:00 AM)

"If anyone bought/claimed RPS Runner, you might want to contact the developer in order to receive a Steam key for it."

[Old] (If something is removed, let me know and i will remove it).
Bouncy ball lite https://boogaeye.itch.io/bouncy-ball-lite (download only)
https://hereingermany.itch.io/jelly-fullversion
https://manstersoft.itch.io/chimera-crusader
https://manstersoft.itch.io/fun-pak
https://manstersoft.itch.io/koala-quest
https://manstersoft.itch.io/oatboy-vs-slime-mold
https://manstersoft.itch.io/poopy-pak
https://manstersoft.itch.io/turtluv2
https://itch.io/s/8871/a-show-of-hands-is-free (claim)
https://rbogames.itch.io/haul (claim)
https://cheesy-walrus.itch.io/shapeball (download only)
https://variantexponent.itch.io/eletors-continuity-effort (download only)
https://itch.io/s/8236/getting-the-game-out-hoping-to-raise-some-funding (Nonnative, download only)

[Sale Ended]
Broken Armor & Shotgun Legends https://itch.io/s/7701/100-off (with claim, Ends June 21st 2018 at 6:00 AM)
(In Steam these two games costs 3,99€ each)
Yellow Snow https://itch.io/s/12089/free (with claim, Ends June 22nd at 4:00 PM)
9 to 5: Overtime https://itch.io/s/10978/free-to-play-summer-warm-up (with claim, Ends June 24th 2018 at 5:59 AM)
S.Q.U.A.R.E. Rebirth https://itch.io/s/12314/123 (download only, Ends June 25th 2018 at 12:00 AM)
POLAR https://itch.io/s/12315/1232 (download only, Ends June 25th 2018 at 12:00 AM)
Superstatic https://sleepystudios.itch.io/superstatic (download only)
Boingkid https://itch.io/s/9400/play-boingkid-4-free (with claim, Ends June 14th at 7:00 PM)
9 to 5 https://itch.io/s/10978/9-to-5-free-to-play (with claim, Ends June 13th 2018 at 5:59 AM)
Von Bottom's Hoard https://itch.io/s/12043/free-rpg-day-have-von-bottoms-hoard-for-free (with claim, Ends June 17th 2018 at 8:00 AM)
Trolley Follies https://itch.io/s/12029/initial-itchio-release-sale (with claim, Ends June 18th at 6:00 AM)
Benjamin of Blackstone Edge https://itch.io/s/11263/birthday-present (with claim, Ends June 6th 2018 at 6:00 PM)
Build To Survive https://itch.io/s/11293/build-to-survive-free-week (with claim, Ends June 8th 2018 at 12:00 AM)
StopTime Drive https://itch.io/s/11272/stoptime-sale (no claim, download only, Ends June 3rd 2018 at 9:00 AM)
Number Islands: https://thebdrive.itch.io/number-islands (claim, Ends May 31st 2018 at 9:00 AM)
Spycon https://itch.io/s/10433/secret-sale (price changed to $0.02 with claim, Ends January 30th 2019)
Killboard https://itch.io/s/11230/killboard-is-free (with claim, Ends Saturday at 6:00 AM)
Super Cave Boy https://itch.io/s/11228/super-cave-boy-super-free-week (with claim, Ends Tuesday at 9:00 AM)
"ERROR" + 2 E-books https://itch.io/s/11172/pwyw (with claim, Ends Wednesday at 11:00 PM)
Into The Myst 2:The Cult https://evilrick.itch.io/into-the-mist-2-the-cult (with claim, until monday at 12:00Pm the game is free)

http://www.opiumpulses.com/store/2014/ryan-silbermans-free-pcmobile-bundle (7 games for free, just add to cart and order).
Note how much points you have and you could buy other stuff with it for free, for example:
http://www.opiumpulses.com/store/2018/ryan-silbermans-cheesy-pcmobile-bundle 250 points (Itch.io)
http://www.opiumpulses.com/treasure/1779/mahjong-with-memes coins 99 points (Itch.io)
http://www.opiumpulses.com/treasure/1708/rebuild-the-european-union 99 points (Itch.io)
http://www.opiumpulses.com/treasure/1740/luke 99 points (Itch.io)
http://www.opiumpulses.com/treasure/1702/space-journey 395 points (Steam)
http://www.opiumpulses.com/store/837/alien-isolation-last-survivor-dlc 660 points (Steam)

Their search is flaky, and i only found them through suggestions, if you come across other worthwhile ones below 1000, let me know.
http://www.opiumpulses.com/treasure/index

There are always plenty of free games on itch.io here without claims.

Last, you can find some itch.io keys on a marvelous site, that you can keep, but can't post due rules.