I use (and abuse) TaskWarrior and Taskopen
Some examples of use:

• Adding a task

  task add ExampleName

• Display the list of tasks

  task

  Output

  ID Age Project             Tag    Recur Description                    Urg 
   3 7s                                   ExampleName                       0

• Annotate directly

  task 3 annotate Nice Annotation

• Annotate using an external file

  task 3 annotate /path/to/file

• Annotate using an url

  task 3 annotate http://arnaud.fortier-family.com

• Tag a task

  task 3 modify +NiceTag

• Open notes

   taskopen 3
   
  Please select an annotation:
      1) /path/to/file ("ExampleName") -- 3
      2) http://arnaud.fortier-family.com ("ExampleName") -- 3
  Type number(s):

Other nice examples:

• http://taskwarrior.org/docs/best-practices.html
• http://taskwarrior.org/docs/tags.html Tags
• http://docs.slackware.com/howtos:general_admin:taskwarrior
• https://github.com/burnison/tasksync Google Task Sync