There are many plugins to choose from. It's hard to know exactly which ones may suit your personal needs. Some plugins do amazing things, while others seem to be of little use at all. This list is not definitive by any means. It is, however, a good roundup of some of the more interesting ones. This, of course, is a matter of preference. Your list may look a little different depending on your preference.
Pyrochild plugins is a series of 20 plugins that will greatly enhance your creative flow. The developer asks for a $6 donation, and it is well worth considering this based on what it does. The plugins can be found at http://forums.getpaint.net/index.php?/topic/7291-pyrochild-plugins-2012-9-16/.
MadJik' all plugins is a pack of 60 plugins, which are far too numerous to list here. There are many plugins here that do interesting things to your photos. They can be found at http://forums.getpaint.net/index.php?/topic/7186-madjik-all-plugins-last-updated-2012-01-01/.
The BoltBait's plugin pack has 21 plugins and a palette file that give you a lot of toys to play with. The developer asks for a donation of $6. That's about $0.35 a plugin, which is not a bad deal. BoltBait's plugin pack can be found at http://forums.getpaint.net/index.php?/topic/8318-boltbaits-plugin-pack-updated-december-12-2011/.
The Photoshop PSD file plugin allows you to save and open Photoshop files.This plugin makes Paint.NET cross-platform and very powerful. It can be found at http://forums.getpaint.net/index.php?/topic/18128-photoshop-psd-file-plugin-newest-version-230/.
dpy's Pack is another large pack of plugins, including some really nifty text effects. It can be found at http://forums.getpaint.net/index.php?/topic/16643-dpys-pack-2012-08-26/.