If you're an avid online shopper, your email inbox is likely stuffed with discount offers as online retailers gear up for what will likely be the busiest shopping day of the holiday season.

As has been the trend this season, the deals are going well beyond free shipping to include markdowns of 25 percent or more. Check out these deals:

• Children's retailers One Step Ahead and Leaps and Bounds are offering 40 percent off already marked down toys and winter clothing, which means shoppers can save as much as 80 percent some items on Monday.
  
• Red Envelope is emailing some of its customers a 25-percent-off offer that excludes its Bose products, but does not require a minimum purchase.
  
• Flowers more your style? 1-800-Flowers.com is offering 30 red and white tulips with a free vase and chocolates for $29.99.
  
• Gap is offering $20 off and free shipping for purchases of $100 or more. This includes items that already have seen discounts of 40 percent off.

Several retailers, including Kohl's and Toys R Us, are doing Christmas countdown sales, with new deals offered each day.

All of these promotions are aimed at jumpstarting online sales, which hit a lull the week after CyberMonday, which is the Monday after Thanksgiving.

According to ComScore, $19.44 billion has been spent online this holiday season through Dec. 12. That's essentially the same level compared with the corresponding days last year.

Sales in the early days of the season, the 12 days beginning with Dec. 1, were up 3 percent compared with the year-ago period. But then sales from Dec. 8 through Dec. 12, fell 1 percent, although Dec. 9 was the highest online spending day on record.

ComScore Senior Analyst Andrew Lipsman expects today, Dec. 15, will be the busiest online shopping day of the season. This prediction is based on the trend of typically heavier shopping on Mondays and the date's proximity to the Christmas, which is quickly approaching.

One factor that could spoil this trend is a big push by online retailers to promote Dec. 18 as a free shipping shopping day.

Although shopping patterns have been more volatile this year, the trends have not swayed ComScore from making any changes to its prediction, which calls for flat year-over-year growth for the season. That's a huge disappointment for the sector, which has consistently seen annual gains at or above the 20 percent range.

The biggest winners in terms of customers visiting their Web sites have been Amazon.com , Wal-Mart and Apple , ComScore said. (Although they can't say whether the higher traffic equals higher sales.)

"To perform well, you either have to offer great prices, as in Wal-Mart's case,"  Lipsman said. "Have the hot product, which Apple does, or in Amazon's case, be a leader in terms of execution."

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