RND2110 READYNAS DUO NAS from NETGEAR is a cheap 2 bay NAS with some good features. Cheap in this case is less than 200 US dollars for a NAS with 1 TB storage.
The RND2110 is in my opinion a good beginner NAS for home users. For business I definitely recommend a Synology NAS or a QNAP NAS that will provide more features for business use.
When you buy the RND2110 you will get 1 TB hard drive but it is possible to add another hard drive and I do recommend a NAS with at least two hard drives in order to use a RAID 1 so disk failures is handled properly.
What I do like about the RND2110 is the rock solid NAS chassis like the QNAP NAS devices.
The power consumption is bad. 60 W is way to much for a 2 bay NAS.
My LAN and WLAN is always turned on so my Apple Airport Extreme is running 24/7 and it is a very good at that. The WLAN covers most of my house but there are some places where the signal is low so I have often needed some sort of a wireless network repeater.
I am not a big fan of WLAN because a WLAN is less secure than a LAN. But the WLAN is extremely nice to have and when you can sit in the garden with your MacBook and access your NAS it makes sense.
The Apple Airport Express device is a easy way to extend the current WLAN and even provide a new feature: AirPlay. With AirPlay you can connect to iTunes on your MacBook and play music anywhere in the house that has some sort music device.
I find Airport Express very useful as the device can be placed almost anywhere it just needs some power in order to function. The Airport Express can not act as a repeater unless the current network is an Airport network. I was a bit annoyed when I heard that.
I definitely recommend the Apple Airport Express if you want to extend your current WLAN.