MS Office is nice but expensive.
Alternatives (multiplatform):
+ OpenOffice (3.1.X stable; 3.2 crashes with DOCX files (no fix yet); 3.3 in RC phase) download
+ LibreOffice (OO fork in Beta stage; nobody is certain about Oracle intentions) download
Only for Linux:
KOffice
GnomeOffice
For Mac:
NeoOffice
