Ethereum Wallet is an Ethereum UI client that lets you create account, send ether, deploy contracts, invoke methods of contracts, and much more.
Ethereum Wallet comes with geth bundled. When you run Ethereum, it tries to find a local geth instance and connects to it, and if it cannot find geth running, it launches its own geth node. Ethereum Wallet communicates with geth using IPC. Geth supports file-based IPC.
If you change the data directory while running geth, you are also changing the IPC file path. So for Ethereum Wallet to find and connect to your geth instance, you need to use the --ipcpath option to specify the IPC file location to its default location so that Ethereum Wallet can find it; otherwise Ethereum Wallet won't be able to find it and will start its own geth instance. To find the default IPC file path, run geth help, and it will show the default path next to the --ipcpath option.
Visit https://github.com/ethereum/mist/releases to download Ethereum Wallet. It's available for Linux, OS X, and Windows. Just like geth, it has two installation modes: binary and scripted installation.
Here is an image that shows what Ethereum Wallet looks like:
