ERUNT - Lars Hederer - Screenshot

If you are using an NT-based operating system, ERUNT is a necessity: Microsoft, in their infinite wisdom, decided to remove the automated registry backup option (available in 9X/ME) from all versions of Windows using the NT Kernel, including XP. However, by installing ERUNT, you can create numerous time dated backups of your registry, which can be restored at any time with the click of a button. The program itself comes in at a very cool 761kb for the self installing exe, or just 462kb for the zipped version. Once installed, the backup creation process is simplicity itself: just double-click the ERUNT.exe and follow the prompts. By default, the files are saved to the Windows directory - this makes things easier if you ever need to use the Recovery Console, or a DOS based boot disk, to restore the registry on a non-booting system. Normal restoration is carried out by navigating to the saved files folder, selecting the date to which you wish to restore, and double-clicking the ERDNT.exe. The program also supports automated backups through command line switches for the more experienced user (details of which can be found in the help file). Another great feature of ERUNT is the inclusion of the registry optimizing tool NTREGOPT; just double-click the exe and follow the prompts to defragment the registry, which increases your system's performance. A very handy program!

RegSeeker - Hover, Inc. - Screenshot

RegSeeker is a freeware tool that does much more than just scan the Windows Registry for invalid entries; it is in fact a whole suite of tools, offering easy access to startup entries, uninstall information, history lists for typed urls, index .dat files, and access to installed colour schemes and IE favourites. One option I really like is the Keyword search tool; while very similar to the "Find" function in Regedit, the tool has several more options, making refined searching possible (invaluable when tracking down those elusive spyware entries). There is a tweaking tool included, offering access to several hidden functions in Windows. Personally, I found this very basic and limited, almost as if the author has thrown it in as an afterthought; if you're after OS tweaks, I would suggest using the excellent (and free) X-SETUP PRO, which offers nearly 1700 registry hacks. Then, of course, there's the Registry cleaner itself, which searches for invalid and unused entries, missing files, and bad references, giving you the option to delete all or just the ones you feel comfortable with. Bear in mind: if you haven't cleaned your Registry for a long time, the list may run into the hundreds, which can prove tiresome to sort through individually. From a purely personal point of view, I have installed RegSeeker on many PCs, and have always deleted all entries found without suffering any ill effects. This doesn't mean it can't happen; so, as with any program that deletes items in your registry, you must be prepared to accept the risks (if you have any doubts whatsoever, please consult with the helpful technical people here in the support forums before deleting anything).
To summarize: this is a very nice set of registry tools, offered free of charge, has a very user friendly interface, and comes in at a tiny 307kb download. I would, however, be wary recommending this program to the complete novice - some knowledge of the Registry and how it works would be preferable.

***WARNING: Always backup your Registry before editing, deleting, or otherwise modifying any Registry entries! Failure to do so may prohibit the recovery from serious problems, which may require you to reinstall your Operating System.