Mods are a grreat way to build your forum the way you want. Mods enable you to have even further control over your forum, you can make users have to have a certain amount of post before they can see or read a forum, you can add a Shout Box which is a chat box that anyone can leave a message. You also can change default settings to make your forum like you want. But as most things in forums, it requires FTP access, once you get FTP access you can do anything with your forum.
PHPBB Mods- This site is the official Modifications site for phpbb forums, they have a great variation and most Mods can be found there.
PHPBB Styles- This site is one of the greatest support, Mods and Show Off forums in the web, also they provide a request forum so you can request Mods, they have a great group of coders that take care of that.
Double Post Protector- What this does is protect your forum of Double Posting, makes the Post botton case sensitive and can be only clicked once
Upload picture to post- This Mod shows a Browse Box under your post while you are making it so you dont have to go through the problem of finding an external image host
Super Cash Mod- Now what this does is adds Cash to your forum, every time someone post they get a certain ammount of "Forum Money" which is good because most people get into it and want more forum money wich means more post for you.
BB Code Positioning- Well I dont know if most of you have noticed but when you are making a post and you forgot to put a BB Code, then you click at the top but as much as you try the BB Code still shows up at the bottom, this mode will make the BB Code appear where the mouse cursor is positioned.
Hope this helps !