Letting visitors post from form

I’m looking for something where the admin can create a form and let the visitors post. Maybe something like:

Wanna come to my party? Fill in the form:
<form method="POST" action="?????">
Name: <input type="text" name="name" /><br/>
Email: <input type="text" name="email" /><br/>
Comment: <textarea name="comment"></textarea><br/>
<input type="submit" value="Join party" />
</form>

How do i make this the right way? I would, in this case, collect these values and store them in an external table in the db. Should i let the users post through “admin-post.php”, should i point the action to the current url and collect the $_POST? Can i add a nonce-filed for preventing bots and stuff to post to this url?

My question is really; Does anyone know a goo tutorial for best practice regarding this, or knows of a nice plugin which lets the users creates their own forms?