What's the difference between bitcoind and bitcoin-qt? Different commands?
You can either run bitcoin-qt or bitcoind, not both at the same time (the Qt part is not just a frontend on top of the RPC code, it uses the core directly).

You can however run Bitcoin-Qt with the -server command-line switch, in which case it will also expose an RPC service (essentially functioning like bitcoind in addition to the GUI interface). The RPC console inside the GUI has the exact same functionality as the bitcoind RPC client.

PS: bitcoind is both an RPC server (when started without RPC command on the command-line) and an RPC client (when started with RPC command on the command-line), while Bitcoin-Qt only optionally runs an RPC server (when started with -server).

Update: In version 0.9, bitcoin-cli was added with just the RPC client functionality from bitcoind. In version 0.10, this functionality will be removed from bitcoind. This means that the following ways of interacting will be possible:


bitcoin-cli or an external RPC client talking to bitcoind.
bitcoin-cli or an external RPC client talking to bitcoin-qt -server.
Using the RPC console in bitcoin-qt.