I went to see Beck once, got there early to find the Cardigans opening. they proceed to open with a very slow, half speed, mellow acoustic style Iron Man.
I saw Bon Jovi open for .38 Special. Didn't seem like a strange pairing til after the show when I realized Bon Jovi upstaged .38 Special big time and the end of an era and the beginning of another were happening.
When Layne Staley of Alice In Chains started officially going down hill, they cancelled their concerts with Metallica, so I ended up seeing Candlebox (aka Far Behind) and Metallica. Kind of strange. And Alice In Chains was the primary reason my friends and I were going, although Metallica put on the most impressive concert performance I've ever seen.