I started using Ocado recently and was pleased to see they have an Android application (as well as one for the iPhone). The interface is very clean and simple to use but has some great features.

My favourite feature is that you can scan wrappers before you throw them in the bin. The barcode scanner matches the product in their online catalogue and you can then add the product to your shopping list for the next order. This process generally works seamlessly and makes it very easy to build up your shopping list. You can also do text based search and, for more recent devices, voice based search for products.
Customer services are also great if you have any issues. I had a voucher code that didn’t work the first time around and they added the free item to my next order with no complaints. If you haven’t used Ocado before then make sure you use this voucher (do a search for ‘Ocado voucher’ if it has expired).
I’ve seen some issues where if you do a search or scan a barcode while it is downloading a new catalogue it can hang. Hopefully they will sort this out on future revisions. Currently though it is still very good and worth a try if you are OK to pay a bit more for your shopping. I’ve used Tesco.com before whose own brand products are certainly cheaper. However, they don’t yet have such an elegant solution for Android although based on this link they seem to be taking Android and QR codes seriously.

Download Ocado on the Go from Android Market
[I have no affiliation with Ocado]