ChemPencil and ChemEquate
ChemPencil is an inexpensive chemical drawing application that has all the usual chemical drawing tools. However as fas as I can tell it does not currently support round-trip editing, structures are pasted into documents as images and can not be then copy and pasted into ChemPencil for further editing.
There has been an update to ChemEquate automatically formats and balances chemical equations. Copy with one click for use in word processing applications. Molecular weights are also conveniently provided.