To help spice up the practice of estimating products, I've created some color-by-number sheets for my students. I like to come up with stupid little pictures because they can't predict the final picture. If you'd like, you could use your own coloring sheet and just add my numbers.
Not only is it just a few problems, but it provides an answer bank, which motivates the students to keep trying and correct their errors. This allows for independent and station work.
Honestly, some students do not enjoy coloring, so I don't require it; however, it's a nice distraction for some students, and has the potential for quick assessment.
Color-By-Numbers: Estimating Products
Color-By-Numbers: Multiplication of Whole Numbers
Color-By-Numbers: Multiplication of Decimal Numbers
I've also listed them separately--with previews.