1st: New Year - This is a great time to look for post-holiday sales, since stores still have lots of inventory left over from the big holidays!
14th: Valentine's Day
17th: St. Patrick's Day

March – April: Easter

1st: April Fool's Day
Second Sunday: Mother's day
Last Monday: Memorial Day
Third Sunday: Father's day
4th: US Independence Day
Amazon Prime Day - Amazon.com recently started 'Amazon Prime Day' in July of 2015. There are tons of deals on all types of products, and the deals run all day!

Back to School Sales (all month long) - This is a great time to stock up on school supplies, toys and clothing for children!
First Monday: Labor Day - For US stores, this usually marks the beginning of the new season, so keep an eye out for great sales on clothing from the previous season!

31st: Halloween - Make sure to check back right after Halloween too, to load up on costumes & other seasonal items. They go on sale the day after Halloween in the US and are usually heavily discounted after the holiday!
Fourth Thursday: Thanksgiving
Day after Thanksgiving: Black Friday & Cyber ​​Monday - This is the biggest shopping weekend of the year! Almost all online retailers will have heavily discounted deals all weekend long, as well as 'doorbuster' deals that only appear for a brief time (usually right around midnight EST) and have ridiculous prices for some items.
25th: Christmas Holiday