is there a way to add dependents with out using the mouse?
 

so as i am entering my list of tasks, when i hit return/enter, it just enters the next task, is there an easy way to add it as a dependent?

cmd-} (a.k.a. cmd-shift-]) to enter a child task;
cmd-{ (a.k.a. cmd-shift-]) to enter an “aunt” task (i.e. outdented from the currrent task)

If you turn on the dependencies column in your view (View->View Options or cmd-J) you can type in the dependencies you want by typing the task id and then a two-letter code for the dependencies type. If you put "type a dependency code" into the search box in the OmniPlan help command, you'll get a link to the page that shows examples.

If you simply want to put finish->start dependencies on a long list of items which are entered in order, type them all in, select the whole group and click the Connection button to connect them all. Yes, it uses the mouse, but not much :-)

I couldn't tell from the original question whether you wanted the indenting/grouping stuff (what jonwhite gave you) or the actual dependency stuff (what I gave you). I think it is worth pointing out that the indenting/grouping stuff does NOT establish a rigid ordering/dependency -- if the two tasks in a group are assigned to different resources, they won't necessarily be scheduled in top-down order.