Nested comments I built on my first rails project before deciding to use disqus instead.

_comment.html.haml

.comment{:class => "c" + nesting.to_s}
	.profile
		%img{:src => "/assets/profile_image_sample.jpg"}
	.message
		.username
			- if defined? comment.user.username
				- if comment.user.username.blank?
					= comment.user.first_name
				- else
					= comment.user.username
			- else
				= comment.user.first_name
		= comment.content
		.reply-link
			= link_to "Reply to comment...", post_path(:original_id => comment.id)
- if @original_id.to_s == comment.id.to_s
	.comment{:class => "c" + nesting.to_s + " reply"}
		= render "submit_comment", :nesting => nesting
- if comment.replies.count > 0
	- nesting = nesting + 1
	- comment.replies.each do |comment|
		= render "comment", :comment => comment, :nesting => nesting

comments_controller.rb

class CommentsController < ApplicationController
	def create
		@user = User.new(user_params)
		@post = Post.find(params[:post_id])

		respond_to do |format|
	      	if @user.save
	      		@comment = Comment.new(comment_params)
	      		@comment.user_id = @user.id
	      		@comment.post_id = params[:post_id]

	      		if @comment.save
	        		format.html { redirect_to @post, notice: 'Comment was successfully created.' }
	        	else
	        		format.html { redirect_to @post, notice: 'Comment was successfully created.' }
	        	end
		  	else
		   	 	format.html { redirect_to @post, notice: 'Comment was successfully created.' }
		  	end
		end

	end

	private
	def user_params
		params.require(:user).permit(:first_name, :email)
	end

	def comment_params
		params.require(:comment).permit(:content, :post_id, :original_id)
	end
end