Once I knew I'd be getting hundreds of thousands of photos stored, back when I first started digital photography, I decided to just use the native Windows folder systems with a standardized naming convention for the files, since I have always been familiar with the Windows folder systems and find it very quick and easy to navigate.
Each batch of photos are loaded to a new folder in the main Photos folder, named for the place or event and date. ; For example, C:/Photos/Disney World 2010-01 (4-digit year, and 2-digit month). ; That allows the photo folders to sort by subject, and further to stay in date order.
Then when I load all the photos from the camera to the newly named folder, I batch name the photos similarly: Disney World 2010-01 001, Disney World 2010-01 002, etc.
If the subject is one I shoot often, I may use subfolders to separate what may be dozens of folders from the same place...so I have a main Disney World folder, a main Wakodahatchee (my bird place) folder, a main Cruises folder, etc...then under each of those, I have the subfolders for each trip (Disney 2009-01, Disney 2009-06, Disney 2009-09, Disney 2009-12, etc).
Then for the final separation...I leave all original photos in each of those files untouched, in case I ever want to go back and reprocess or rework a shot...as I process shots, I load them into a subfolder called 'Processed'. ; When I want to slideshow my final processed shots, that's the folder I'll use.
The whole thing lets me keep all my photos in one folder called 'Photos', yet separated within by subject and date, original and processed. ; Using basic Windows search capabilities, I can search through the folders by date, name, subject, or camera used. ; Some photos I took the time to tag for additional searches, but I get a little lazy with that.