Ulead Particle Plug-in: This one is the cause of nearly all of the rain effects I have in my drawings. Aside from rain though, it has sparkles, bubbles, clouds, smoke, fire, fireflies, and snow! It's very easy, very small and available for free now!
Luce: Luce is actually one of my more recently discovered Plugins, but I found it useful none the less. What it does is sets a back lite glow to anything deemed "light" in color, such as white. A good example would be the moon's glow seen here notice how things seem to "beam" through in the background? That is an effect Luce creates, but you could of course achieve the same effect without Luce with a little work.
Alien Skin's Eye Candy 3: Is apparently free O_o' I did not know this. Normally Alien Skin's Plugins are quite expensive, but this one is apparently free. I have used this for everything practically... everything from making strange swirled effects (not unlike ones found in screen tone mangas- hint hint) water reflection effects, fur effects, glass, fire, water droplets, smoke effects... well the list is there you can read xpx lol (I hope... how are you reading my tutorials if you wheren't =_=?)
Ulead Fantasy Warp: Another Ulead product that became available for free. This one is interesting in that it takes images and "warps" them into all sorts of different ways. mostly mirroring them any number of ways you want. Not useful in most cases, but can achieve that twisted/mystical background, or give a soft mirrored effect.
Harry's filters: I've actually had this one awhile, and have had mixed results on it. On the one hand, it has a TON of little plug-ins to it that can create some pretty interesting effects-- on the other hand it has a TON of little plug-ins that can be overwhelming and a little irritating if you happen to use a lot of different plug-ins. Unfortunately, I can't pin point any specifics as to what makes this useful because the different plug-ins can become useful only in specific cases. If you don't mind spending a lot of time experimenting with different effects, check this one out.
Kang: Similar to Harry's Filters except it boasts some very... strange warping effects. It's as if Harry's Filters married Ulead Fantasy Warp, and this is what came as a result. It's another one of those plug-in sets that have a lot to them, but maybe only be useful every now and then unless you plan on making a lot of uniquely twisted backgrounds. Again, you'll probably spend a lot of time playing around with them because there's so many.
Little Ink Pot: This would technically be more specifically used for things like Photos, but you wouldn't believe how something like this can become quite useful for normal artwork, both in digital art and scanning. It comes with three plugins particularly, Xpose which can be perfect for making scanned artwork look brighter in color easily without messing with photoshop's settings, Thredgeholder which turns photo images into "sketches" which in turn could be used to help get a better idea of how to draw things, and Chalkaholic, which honestly? I dunno. Nothing in particular comes to mind on how it could be used...lol
Virtual Photographer: Another Photo-based plugin, but has some nice settings for colors, bloom, brightness, contrast, and even film grain. It could be useful for those who scan their work, but maybe want to clean up some of it, or tweak the colors a bit more when their scanner "killed" them, or want to add a little something extra.
