There is a plug-in that I have installed on every single site that I operate. And that plug-in is Gravity Forms.
In a nutshell, this plug-in will allow you to make web forms on your blog. At first glance, it seems a bit boring and unrelated. The only form you think you might want is a contact form – and there are several free contact form plug-ins out there already.
But, let me tell you a little about Gravity Forms…
In my post Why Buy A Premium Forms Plug-in For WordPress?, I spell out several of the different ways to use a plug-in like Gravity Forms. As you can see, this goes way beyond contact forms.
As for alternatives to Gravity Forms, I honestly couldn’t find any that hold a candle to it. The only one I found that looked promising is called Formidable Pro. I don’t have any experience with that plug-in. It looks nice, but I don’t think it has the recognition and support that Gravity Forms does. For example, the existence of the add-ons for Gravity is a selling point, in my eyes.
Gravity Forms is, without a doubt, the best form plug-in for WordPress. You’ll be coming up with new ways to use it in your business all the time. I guarantee it.