[jewbacca]

Softer entry to the whole concept of lvalues/rvalues in general:

http://eli.thegreenplace.net/2011/12/15/understanding-lvalue...

[mpweiher]

And of course there's Strachey's Fundamental Concepts in Programming Languages (1967), which introduced the LValue/RValue distinction. It is very readable and relevant today.

http://www.cs.cmu.edu/~crary/819-f09/Strachey67.pdf