.htaccess

You can place a .htaccess file in a directory serviced by apache to override server default behaviors without needing to alter httpd.conf or even to restart Apache - assuming, of course, that the directory in question has been allowed override privileges for the things you want to do!

For example, assuming mod_rewrite is installed and available in Apache, you can do the following in the .htaccess file in the root of a site to redirect an insecure http request to the same site via secure https:

RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI}

Or if you want to block off a pesky spammer-ridden IP block from posting things to a blog or wiki, while still allowing people on that block to READ the blog or wiki or what have you:

AuthName "Anti-Spam Protection"
AuthType Basic
<Limit PUT POST>
order allow,deny
allow from all

# CHINANET telcom - 2006-03-02
deny from 212.0.0.0/8
deny from 216.0.0.0/8
deny from 218.0.0.0/8
deny from 221.0.0.0/8
deny from 61.144.0.0/14
</Limit>

Note that comments - prefaced by # signs - ARE allowed in .htaccess files. Use this to your advantage!

What if you want to require a password for a certain directory?

# require a username and password to get into this lightly secured area
AuthType Basic
# note: it's safest to keep the password file OUTSIDE the webroot!
AuthUserFile ../.htpasswd
AuthName "JRS Systems Personnel Only"
require valid-user
satisfy any

Of course, this requires you to actually have a .htpasswd file in the appropriate location - you can use the htpasswd utility to create one for you.