I used AcidSearch for several years. Since it's not updated any more and made Safari 2 and 3 crashing, I tried Inquisitor and SafariStand (which I disliked) and now I finally found Glims:
http://www.versiontracker.com/dyn/moreinfo/macosx/34506
Glims works very well - substitutes ForgetMeNot, MegaZoomer (what Safari is concerned) and AcidSearch (or Inquisitor). And there are a lot more useful functions.
AcidSearch
Safari search box enhancement
Version: 0.62