I've been growing tomatoes for years. This year, for the first time, I tried a red plastic mulch.  For the past few years, I've mulched with seaweed — it's easily collectible on the little island where I spend most of my summer, and contributes valuable organic nutrients to the soil as well.  But I've been increasingly plagued with Verticillium Wilt, and I'm not able to rotate crops in my tiny 10×10 garden (it's all tomatoes!). So,  I figured a plastic mulch might help prevent the soil-borne fungus from splashing up onto this year's plants.  And I'd read about red plastic mulch increasing tomato yields and decided to give it a try.  Well, my plants are growing faster, bigger and healthier than ever — at a time when everyone else is complaining that their tomatoes are not growing as well as they usually do with the rainy weather we've had.  I bought Dalen Better Reds Mulch Film
from Amazon.com.  While it's easiest to put the mulch down when you're planing the plants, these 3'x3' film squares are easy enough to place around plants already in the ground.
See my other garden tips and gadgets here.