I would only recommend that Advanced & Expert users use these snippets!
This small collection of .htaccess code snippets are things that I’ve picked up over my time on the web for very specific uses. The .htaccess file is very dangerous to the wbesites health f you do anything wrong so I highly recommend that you fully backup everything before starting to use any of this code.
1. To Remove the generic /category/ slug in your category URLs
RewriteRule ^category/(.+)$ http://www.yourblog.com/$1 [R=301,L]
Source: How to: Remove /category/ from your WordPress url
2. Stop Spammers in their Tracks with Comment Deny for No Referrers
RewriteEngine On
RewriteCond %{REQUEST_METHOD} POST
RewriteCond %{REQUEST_URI} .wp-comments-post\.php*
RewriteCond %{HTTP_REFERER} !.*yourblog.com.* [OR]
RewriteCond %{HTTP_USER_AGENT} ^$
RewriteRule (.*) ^http://%{REMOTE_ADDR}/$ [R=301,L]
Source: How to: Deny comment posting to no referrer requests
3. Ban Spammers from your site when you know their IP address
order allow,deny
deny from 200.49.176.139
allow from all