Crochet Pattern Central is a great place to find quality free crochet patterns, including vest patterns. You can find links to a variety of vest patterns by looking under both the "Women's Clothing" and the "Men's Clothing" sections in the directory. Locate the directory here: crochetpatterncentral.com/directory.php.
Crochet Pattern Central does not host the patterns itself. Instead, it provides a huge database of links to free patterns on other websites. Most of the patterns that Crochet Pattern Central links to do not require you to create a login account. For your convenience, the directory always marks those sites that do by placing a plus sign (+) before the link.