I have all of their albums Mairi, and saw them live twice - undoubtedly the best live act I've ever witnessed. For me they're the best band Britain produced after The Beatles. A good starting point would be one of the many "greatest hits" compilations available - try "Feel The Noize" from 1997, which succinctly covers the broad span of their career and includes their 15 top ten UK hits (including all six number ones and the four hits which peaked at #2).
From their glam/pop era try "Slayed?" (1972) "Old New Borrowed And Blue" (1974) and "Slade In Flame" their 1975 film soundtrack. All terrific.
By the late 70s and into the 80s they were much more rock orientated, "We'll Bring The House Down"(1981) and "The Amazing Kamikaze Syndrome" (1983) were both fabulous albums. By the mid 80s their output was pretty uninspiring; their last couple of albums really aren't up to much in my opinion.
Of their live albums, try "Slade Alive Vol. Two" (1978)... it's a belter!
Hope that helps, and do let me know what you think!