Sachin Khosla

This plugin will allow you to remove the URL option from the comment box. This prevents automated bots to post spam links on your website. It helps your website retain the SEO Juice. 
This is a lightweight very simple plugin. No Javascript, ajax hack.
<h3>Usage</h3>
Simply activate the plugin and the URL input text box will not appear.

Disable / Hide Comment URL

Disable/Hide Comment URL lets you hide the URL/Website input field from the WordPress inbuilt comments block.

Budiony Damyanov

Counts the visits from web spiders, crawlers and bots in your blog, with ability to get the blog rankings from Google or Alexa. 
Also can count any other visit, the plug-in is looking for patterns in user-agent string, which pattern can be customized. 
You can block or unblock crawler, spider (or any other item), by IP address and identifier via .htaccess file. 
As additional information you can get your blog rankings from Google PageRank or Alexa.

bodi0`s Bots visits counter

Counts the visits from web spiders, crawlers and bots in your blog, with ability to get the blog rankings.

Disable / Hide Comment URL vs bodi0`s Bots visits counter