I am looking at building an application using Bitcoins, and being a newbie the only real resources I have found regarding how to interact with the network is to issue RPC commands to the bitcoin-qt client running as a service.
I've played with this a bit and I am curious if there are other clients that do the same thing? Or is this client the only game in town?
You have many options but Bitcoind is a popular one due to its initial ease.
No, it's an important part, but it's not the only option. And it depends entirely on what type of application you want to build and where you are located geographically.
Running bitcoind exacts a certain toll for hosting fees as well as managing security. It's what I've chosen for my business, but it's not the only approach for everyone.
While @ChrisW's answer is good for situations where you need basic functionality, you have to remember that you'd be relying on third-parties. Which means when they go down, also your application goes down.
It depends on what you need to do, but if you're just looking to send and receive bitcoins and checking balances there's for example bitcoinj which is a Java implementation that you could use within your application without having to rely on a full-node (bitcoind).
This would be a lot faster and easier in my opinion if you're just building a wallet application for example, because it's not a full node and doesn't require you to download the entire block chain, but just the headers.
