Io (http://www.iolanguage.com) is a bit of an exception then.

Its homoiconic but its not a Lisp. And it doesn't have macros yet its code is fully inspectable/modifiable at runtime in an very easy & elegant way.

For eg. if you wanted to have a line like this:

    list(1, 2, 3) each foo bar

which needs to be transformed into below at runtime:

    list(1, 2, 3) foreach(foo bar)

Then this can be done like so:

    List each := method(
	m := call message
	m setName("foreach") setArguments(list(m attached)) setAttached(nil)
	self doMessage(m)
    )

ref: http://www.iolanguage.com/blog/blog.cgi?do=item&id=86