Get an open source, portable, future-proof, simple list:
http://todotxt.comIf you need a bit more complexity, keeping with open source tools, http://www.redmine.org takes care of the job, easily. Plugins are a way to easily tweak it your way.
But falling for SaaS is easy, with http://trello.com, made by the guys at Fog Creek Software - which you might know already through the resounding name Joel Spolsky - is an awesome simple yet powerful tool, both for business and personal use.