Of course I make frequent use of Wikipedia and Allmusic. Both are excellent, but each has its drawbacks, and neither is 100% complete. Allmusic is a better source of album art and sometimes is better at providing track listings and other information about an album. However, Allmusic often gets the composer of a song wrong by listing people that were NOT among the songwriters. Sometimes Wikipedia is really good but is kind of hit-or-miss, as you would expect given how Wikipedia gets its information. Sometimes you get a LOT of information about the artist or album or song, and sometimes it's pretty sparse. In the case of albums, sometimes all you get is the name of the album. By the way, I'm an occasional Wikipedia editor and content creator myself.
Discogs and 45cat are both very good for songwriter info, for release info (year, label, and catalog number), and for label scans. Marv Goldberg's site has tons of doo-wop and R&B artist bios. Soulful Kinda Music is great for discographies of R&B and Soul artists. YouTube, somewhat surprisingly to me, is a valuable resource for information on all sorts of singles and album cuts, plus you can hear what many of them sound like. I'm indebted to all the people who make videos of records being played, and especially those who give a good clear look at the label before it starts spinning.
I know there are other links I'm forgetting to include right now. As I find them again, I'll add them to References.