I'm running phpBB on my site (although a slightly modified version of it, I'm running the PNphpBB module with PostNuke), and i've installed a few hacks on there that have proven to be quite useful...
Some of these could be EXTREMELY useful on here given the nature of this forum's general topic (webmasters)..
First up is a couple of BBCodes.
[google]Search Phrase Goes Here[/google]
GREAT one for the Google & the other search engine forum. Ok, so it only saves a few mouse clicks & typing, but could prove to be very useful - I use it a lot on my site when referring people to search for info on a species of reptile that I've never heard of before.
It can also be just a good general tool. When somebody posts a stupid or asked-100-times-already question, instead of just saying "hit google", which they may have already done but not know exactly what to search for, a reply can simply be "try this, [google]exact term to help with the search[/google]".
More polite, and more useful. I know a lot of people, especially those new to the internet can have a real hard time using search engines (although, yes, they do seem to operate pretty obviously for me as they probably do to most of the people who've had a PC for more than 10 minutes, but there are people out there who have simply never needed to use one before).
[flash]http://url.of.flash/file.swf[/flash]
This also supports a width & height variable in the opening [flash] tag... this could be a useful one for those wanting opinions of banners, logos or whatever in the flash forum, although I could see how this one might be easily abused.
Now, this is one that I really really like (not a bbcode tag)... A "watched topics" page. This is something that's included by default in the user control panel section of vBulletin, and something I really missed in phpBB, but there is an addon available to add this feature.
The output is a little messy, so it'd take a little work to neaten it up to fit the gorgeous theme that is already running on this site, but that's a very hand feature. If somebody's posting on 50 threads a day, their E-Mail inbox can fill up pretty quickly. Can be VERY handy to just check a bunch of boxes, and remove a load of 6-month-old-yet-extremely-busy threads off your watch list.
I'm not sure of the exact URLs of these mods off-hand (although the are all mentioned somewhere on the http://www.phpbb.com or http://www.pnphpbb.com sites), I just have the files that I downloaded, but I can either send over those files to you, or hunt out the URLs so you can download them yourself if you're interested.
Opinions?