Some of my favorite plugins are
Impressionist (free for now; Microsoft use to package it with Office 2000 /w Frontpage, but they no longer support it; man this gem is a must have. Steve {a.k.a., Trimoon} still hosts it on his site; get it while you can).
Paint Engine (not the direct website link, but this site has cool presets) I like, but haven't really used that much of late; still a very cool filter to have (also free). Flaming Pear's
Mr. Contrast (not free, but well worth the money; have a try before you buy version) is one of my favorites; even works well in GIMP. Flaming Pear also has a lot of
free filters too, so visiting their website should be on your to do list. I can go on and on, but the next set should be in your arsenal too.
Xero's free filters are definitely a must have.
EyeCandy too (version 3 is free).
Yes, RetouchPro has some competition. The site I frequent the most is
DPReview's Retouch forum. I also visit
Innographx and Fred Miranda's
Photo Illustration and Digital Art forum (not so much now, but still have friends there).