Is there a good website for finding out exactly when albums and singles were released (i.e., day, month, year) and how well they did on the various charts?

You should try a combination of wikipedia and allmusic

If you want to know about UK charts,there's a complete database at everyhit.com

For complete UK chart runs, go to www.polyhex.com.

http://uk-charts.com/ also has a nice history, and links to histories of many other countries' charts!

Another comprehensive source for world charts is acharts.us.