Nikhil posted his wish list for browsers and scripting.
One thing that I wish for in the CLR world is native support for the "objects as associative arrays" concept that's fundamental to many dynamically typed scripting languages. Being able to access an object's state via either foo.bar or foo["bar"] is tremendously powerful.
It irritates me that converting a structured CLR type into IDictionary<string, object>/IList<object> requires a deep object copy and is thus a linear operation with respect to the number of nodes in the object graph. It would be so nice to be able to convert freely between a statically typed representation and a structurally typed representation in sublinear time.
Viva la expando! (in spirit, but almost certainly not in practice)
Update: fixed typo
