wp-plugins.net and dev.wp-plugins.org currently contain the cutting edge of what's happening with plugins.
be sure to install he latest (2.0.4 as of this writing) version of wordpress and keep it up to date.
each plugin's description should let you know whether it will operate correctly with wp 2.x.x or if it is a 1.x.x plugin (many of those even work with a minor bit of tweaking).
Personally, I've used phpBB for a couple of sites for years, and the WP plugin system is much easier to deal with for one, and is much more secure/less apt to cause problems than phpBB.
I can recall a couple of times where users requested I install specific phpBB plugins which not only didn't work, but also ruined the base installation because as you should be aware, many of the phpBB plugins 'edit' core system files and database tables whereas WP plugins do not, thus making them much safer and easier to use right off the bat. For example, if you installed a plugins that for one reason or another didn't work correctly with your site (I just did one yesterday out of the dev trunk, and the site became a blank white page with one
tag in the source !) simply delete the plugin's file/directory from your wp-content/plugins directory and you're back up and running.
Quite the contrast to something like phpBB where you'd then need to go back and by hand figure out which phpBB files were changed by the plugin, what changes were made, then attempt to return the files to the state they were before the plugin install.
Summary -- overall, you'll find the WordPress plugin architecture much safer and easier to deal with than many other packages out there since plugins do not alter core system files