I usually look at software which provides functions already included in Windows the way I look at bottled water--why pay for what you already get for free? A program which overlaps with built-in functionality has to do a lot more to be worth the price. Of course, it helps if the price is "free," and RegScanner (in 32-bit and 64-bit versions) hits this mark, as well as providing notably enhanced functionality over RegEdit. This registry scanner doesn't replace RegEdit, but it makes it easier and faster to get into your Windows Registry.
RegScanner lives up to its name: It scans the Registry, but it doesn't give you any power to edit it. (Though it will fire up RegEdit when you've found the keys you seek.) While RegEdit gives you "free and barely worth it" tools to find a particular key, RegScanner gives you a "worth paying for, even though it's free" set of features. To start with, RegScanner shows you all found keys at once, rather than forcing you to single-step through found items in the Registry tree. It allows you to filter by data type, to pick any base key, to search for keys added or modified only within a given date (helpful for some security purposes, if you suspect something has been changing keys but you're not sure which ones), and so on. Once the list is complete, you can export all or some of them, create an HTML report, or double-click an entry to open RegEdit for that key.
There are some drawbacks to RegScanner. The "Help" menu item merely displays an "About" box, and double-clicking the .chm file causes an error. If you accidently use the 32-bit version on a 64-bit computer, as I did, you may experience extremely bizarre (albeit non-destructive) behavior--on my system, it locked into a recursive loop in which it kept appending a key to itself. This error did not manifest when I tried an identical search with the 64-bit version. And of course, if you are unfamiliar with the Registry or don't know why you'd want to scan it, this program probably isn't for you.
Several years ago, I had to find and fix a complex registry-related bug. If I'd had this program instead of just RegEdit, I could have fixed the problem in half the time. That's about as strong a recommendation as I can make.