Spider Identification: What spider looks like a black widow in shape, size, and even style of web...?

Quite a few of the various Black Widow species often have the colorful patterns of the young instars even into adulthood. Western Black Widows seem more likely to have a full stripe down the back, while Northern and Southern Black Widows are more likely to have red spots or a broken line than a single stripe. A red spot or stripe with a lighter yellow/whitish outline is fairly common for these spiders, especially in the males or young females. The links show you some representative examples (Western Widows are the last few ones), and you can browse the other pictures on the website.