I need to be able to create a graph image (.jpg .bmp etc) based on two sets of data that I have output to file. They are just simple floating point values, any apps out there that can do this?

OpenOffice Calc? If that's not what you're after, can you clarify?

Based only on that very short description, look at the http://www.graphviz.org/ tools. The tools can generate things from simple line plots of data up through laying out boxes and directed graphs.

Google Chart API. No install, no nothing, just open a page in browser, Save As, ....

This forum isn't cooperating, but the following works
<img src="http://chart.googleapis.com/chart?cht=lc&chd=t:10,80,50,40,200,30&chs=250x100"></img>

Thanks for the replies, I ended up using gnuplot. Works perfect.