In my Dropbox-synced todo list I use the following notation:
[ ] Todo.
[?] Pending feedback.
[>] Currently underway.
[X] Complete. [ ] Todo.
[?] Pending feedback.
[>] Currently underway.
[X] Complete. o task 1 [not started]
/ task 2 [started]
x nested task A
o nested task B
+ task 3 [blocked, e.g. on hearing back from somebody]
x task 4 [done]