After sticking to my N900 for far too long I finally got myself an Android device this summer like I should have 4 years ago (I was quite interested in it back in the day).
Although I've been toying around with Android apps ever since, I've been heavily using one app you probably haven't heard about: Listing It!, made by my good friend Ciske Boekelo.
The neat thing about this list app is that it lets you easily turn an item on your todo-list into a list, with items of its own.
This lets you subdivide your lists any way you see fit: You have your shopping list, but you might want to add an extra level with your groceries listed by which shop you want to by from, or split them up by recipe, or by day of the week. Your list becomes a tree, structured any way you like.
Personally I use it for lots of different subjects. My Aperte tree for example has all my projects per client, with high-level subjects that I need to work on. It also contains a simplified version of my administration, noting which projects need invoicing and which invoices have (or haven't) been paid. My other trees contain stuff I have to get for my car, the daily groceries and all those odd jobs around the home.
All in all, Listing It is a highly useful app in my (biased) opinion. Give it a try and if you find it as useful as I do you can buy the ad-free version for a single euro.