Billboard has revamped their website and included free searches for discographies and chart positions for the last 20 years. Full lists may be obtained with a Billboard subscription. Of course, these may not include the most recent results.
In order to access the info, go to www.billboard.com/bbcom/index.jsp and look under the top bar for music search. It should already be set to artist and then search. When you get you artist you will get a bio page (most of them are fluff provided by the PR team) and you can select a discography page or artist chart history page. Select the latter and under the artist’s picture you will get a choice of singles or albums. Choose one and then choose how to arrange the data and you have it.
You can also go to RIAA at www.riaa.com and search the RIAA sales certs for an artist. Combined with the Billboard info you will actually have truth on your side when you make claims about your favorite. Not that truth has ever had much stock around here anyway. But before you choose to replace the first syllable of your fave’s rival with “flop”, do check to see if it applies.