Besides the Amazon already mentioned, here are a few examples that come to mind:
Abound FCU Visa offers 5% uncapped on gasoline.
Affinity FCU Cash Rewards Visa offers 5% on Amazon.com and bookstores, I believe uncapped, capped at $3500 a month. Plus, members have reported they offer additional quarterly categories .... are those uncapped ???
PenFed Credit Union offers 5 points on gas with their Platinum Rewards Visa and 4 points on travel on their Pathfinder Rewards card for Honors Advantage members. However, points are worth only 0.85 cpp now so that's not 4% and 5%. It's more like 3.4% and 4.25%.
Target Red Card offers 5% on all Target and Target.com purchases.
Walmart Mastercard (Capital One) offers 5% on all Walmart.com purchases.
If you're a Verizon customer and willing to accept rewards in Verizon dollars for credit towards your monthly bill or Verizon purchases, you can earn 4% back uncapped on both groceries and gasoline with the Verizon Visa (Synchrony).
I'm assuming you're talking more about cash back cards with no annual fee, @Neiltyson? When we introduce travel points and transfers to partners for travel, getting 4% or 5% is not uncommon with several premium travel cards.
If you shop at Amazon, there are a couple cards that will give you uncapped 5% at Amazon and Whole Foods.
Also, if you shop at B&H Photo, their Payboo card can knock off the sales tax. For me that's 10.1% and that's not capped. That one is actually huge if you buy electronics.
Elan Rewards+ is the less fancy-named clone of the Altitude Go with 4% uncapped on dining.
Barclays Wynhdam Business card gets 8x on gas. Also includes very lucrative Caesars Diamond status if you're near any Caesars casino. After earning the bonus for this card, I transferred 30k points to Caesars Rewards points waiting for me to spend it at 1cent/pt. Also note - some 711s that have gas stations may code as gas purchases even if you're buying coffee 
The Cardless offerings for sports teams have some weird categories some as high as 7x. Uncapped I do believe.
EDIT: Celtics - 7x rideshare/streaming services 4x bars/restaurants
Cavilers - 5x streaming 3x bars/restaurants/groceries/food delivery
Liverpool - 5x rideshare/streaming 3x bars/restaurants/food delivery
Manchester - 5x rideshare/streaming (and some stuff only on game days, so that's not exactly uncapped)
Marlins - 3x gas/rideshare/streaming/bars/restaurants/food delivery
Pelicans - 4x gas/bars/restaurants/food delivery
Biz - 
@Aim_High wrote:Besides the Amazon already mentioned, here are a few examples that come to mind:
Abound FCU Visa offers 5% uncapped on gasoline.
Affinity FCU Cash Rewards Visa offers 5% on Amazon.com and bookstores, I believe uncapped. Plus, members have reported they offer additional quarterly categories and I believe those are uncapped as well ???
PenFed Credit Union offers 5 points on gas with their Platinum Rewards Visa and 4 points on travel on their Pathfinder Rewards card for Honors Advantage members. However, points are worth only 0.85 cpp now so that's not 4% and 5%. It's more like 3.4% and 4.25%.
Target Red Card offers 5% on all Target and Target.com purchases.
Walmart Mastercard (Capital One) offers 5% on all Walmart.com purchases.
If you're a Verizon customer and willing to accept rewards in Verizon dollars for credit towards your monthly bill or Verizon purchases, you can earn 4% back uncapped on both groceries and gasoline with the Verizon Visa (Synchrony).
I'm assuming you're talking more about cash back cards with no annual fee, @Neiltyson? When we introduce travel points and transfers to partners for travel, getting 4% or 5% is not uncommon with several premium travel cards.
Just a correction on that. Amazon and bookstores are capped at $3500 a month. Which should be plenty for most. However, I got a big purchase coming up of almost $5000 so that will go on my Prime card instead otherwise anything over the $3500 would only earn 1% back.
Bonus categories right now are insanely good. 5% on gas, Supermarkets, and Garden centers, this in addition to normal rewards which are already 2% for gas and Supermarkets and so we are talking 7% overall for those two and 6% overall for Garden centers. The best part, Walmart stores, and Costco stores are included in Supermarkets. Costco with our executive membership is therefore 9% back overall.
@Crowhelm wrote:
@Aim_High wrote:Affinity FCU Cash Rewards Visa offers 5% on Amazon.com and bookstores, I believe uncapped. Plus, members have reported they offer additional quarterly categories and I believe those are uncapped as well ???
Just a correction on that. Amazon and bookstores are capped at $3500 a month.
Thanks @Crowhelm. As I said, I didn't know all the details but I corrected my original post. Are there caps on those quarterly bonus categories that Affinity CU offers? They don't really publicize much if anything about that as far as I know. I've only heard about it from forum members.