I was having trouble making a nice SUBMIT button on a Gravity Form. Looking for help out on the Internet had all kinds of purported solutions, some recommending getting additional plugins and so on. Luckily, I didn't need to add any plugins! We always want to avoid...
I have found that all round best plugin to use for Constant Contact subscribe forms is Constant Contact Forms by MailMunch. It is simple, and has options to create popup forms, add fields, and looks nice.