I gave a small talk on plugins at WordCamp LA recently and was inspired to start compiling a list of my most commonly recommended ones. I’ve also started collecting them as Favorites at my WordPress.org profile but there’s no way to organize them there according to topic or purpose. The list is by no means exhaustive so if you have any requests for recommended plugins of a certain kind, leave a comment and I’ll see about incorporating them into a future edition.
Here’s what’s on there as of now:
Formidable (free and premium)
Formidable has both a free and paid version. The free version is one of the better free form builders available. For me, the workflow and interface is easier to work with than other free plugins such as Ninja Forms or Contact Form 7.
http://webtrainingwheels.com/recommends/gravity-forms/ (aff. link)
Gravity Form is strictly a premium plugin – there is no free version. I have invested in the Developer license and use it on most sites because it’s so powerful. This is more than just a contact form plugin – it gives you advanced data collection and processing capabilities. There are add-ons to integrate with other services such as PayPal, MailChimp and many others. Developers will find it very customizable via the many hooks and filters provided.