I just downloaded this one last night - there is a short trial period before a watermark appears on your clips. Haven't played around with it too much yet -- but it seems to work
Let me know if you try it - and what you think!
There are quite a few available, and New BlueFX probably has the largest array.
What Effect are you looking for?
Because of the number of Effects available, I'd suggest going looking for them, when you need them.
NewBlue FX is probably the #1 supplier for PrE, and I'd look over their portfolio of Effects.
Some other companies, do Effects plug-ins specifically for PrPro and AE, and most might not work in PrE. Check out the compatibility of each, before you even download a trial. Red Giant's Magic Bullet Plug-ins cover a wide gamut of Effects, and BorisFX has many too. Again, in very general terms, most are available for PrPro and AE only - but do check.
Another good source of general Effects is ProDAD's Vitascene. It is available for PrE. It is more of a stand-alone program, BUT can be launched and linked from within PrE.