I've used the Google graphs to find problems with my power usage and distribution for a couple of years now. Nice system. There are other graphing systems out there, but each of them is different from the others and one has to settle on something to work with. I just chose Google, not because it's the best, but because I think it might continue to exist for a while and has reasonable documentation. Oh, it's also free.
At any rate, most of the graphing software takes a table as input. That presents a particular problem for us inexperienced web programmers. What the heck is a table and how do we make one? Once we understand that to some degree, how do we get the data from Xively and put it into a table? This little bit of knowledge is hard to come by. I went through several iterations of trying to get data, format it into something to give to the Google API and see what was displayed. I came up with this:
This is the actual web page I created to display a days worth of data on power usage and outside temperature taken from my sensors. To use it, just copy the code into a file, save it as html (htm, whatever) and then click on it. It'll load my data and give you a graph you can play with. Then, modify it to use your feed id, key, and other stuff to display your own data. It can serve as a template for your own graph as well.
If you want to use it as part of a web page with other information, pictures, etc, just put it into an iframe and include the page. I keep this page on Dropbox so I can use it from anywhere, even my tablet. Some browsers have a little trouble with iframes (chrome) others have trouble with Google charts (Opera, Silk), so your mileage may vary, but it can certainly serve as an example.
This is what you will get with a line like:
<iframe width="100%" height="325" scrolling="No" seamless frameBorder="0"
And yes, the src attribute up there points to the page I have on Dropbox to show this page. Feel free to grab the source directly from there as well.
As I said before, my web programming experience is slim, so there may well be better, more elegant ways to do this. If so, leave a comment for other folks (and me!) to help make our lives simpler. For example, you have no idea what a pain in the butt it was to get this page to work using the tools that Blogger provides. Their editors kept changing things and messing up the display. I finally got it to work, but I haven't tried it on multiple browsers so, it may be messed up. Look at it in FireFox, it seems to be the best with this display.