Lifehacker had some links to try during a Gmail outage:
Plain HTML: http://mail.google.com/mail/?ui=html
Safe Mode: http://mail.google.com/mail/?labs=0
Old version: http://mail.google.com/mail/?ui=1
Bypass browser checking: http://mail.google.com/mail?nocheckbrowser
Mobile version: http://mail.google.com/mail/?ui=mobile
iPhone version: http://mail.google.com/mail/x/gdlakb-/gp/
iGoogle gadget: http://www.google.com/ig/gmailmax
