A couple of visual oddies you should fix:
1) The graphs should have some kind of headers in them. It looks weird without any text on top. Also don't use the budget as min-max, it should be lowest group and highest group (100-1000, not 498-928). It looks very squeezed in there, might want to fix that.
2) Columns with dollars on the right side should be right justified, not left. There's a reason, you know there's always 2 decimals on the right side of the dot, but not the left, so it always look justified. You have it right on the left side, but you need to keep it consistent throughout the application. You also have the budget column that's not right justified.
3) Center the Category Header, so that it's consistent with the Date on the left.
4) Your New and Edit buttons are not consistent in how it should placed. New on Right and Edit on left? It looks weird and out of place.
Overall, it looks nice, it looks like a leather bound budget planner.
Thanks, I agree with your first 2 comments. The choice of header justification was modeled after one of the views in the Calendar app. I played with it in every which way and for now decided I like this way the best. The New and Edit buttons are contextually placed, i.e. the new button adds a new category to the list that the button is adjacent to, and the Edit button edits the active category on the side with the Edit button.