Issue tracking applications that subdivide issues into (sub)tasks?

I am looking for an issue tracking application, which has two levels in its task hierarchy. This is because I find myself very often creating informal "TODO" lists within my issues. It seems to me that a FEATURE is usually bigger than a TASK - one feature usually requires several things to be done - e.g. "check if this sth will affect efficiency", "add the control in the GUI", "implement new extension to the core engine", "update documentation". Without stating all these sub-task, I find it impossible to estimate the time needed and the real complexity of the complete task.

I know I could create several issues, but it is often not feasible because these sub-tasks:

are related to a single feature from the user's perspective,
can be tested only together, when everything is done,
have the same developer assigned-to,
should be displayed together all the times,
should have only two states: todo or done.

Do you know any (commercial or not) applications that allows this? I am not just interested in hierarchies of issues or issue linking, but I need something with full issues on one level and with smaller and quicker "todo" lists on another one.

Solution

Yes, Jira and Fogbugz have subtasks. I have found however no application, where subtasks were something smaller and quicker than tasks - I still have to repeat all the fields of the main task.

I ended up using Project Kaiser and I am satisfied with it. It has quite nice hierarchical subtasks.