First post here by the way. If I'm looking to have my site pull a string of numbers from another site and graph the results on a weekly basis, can you suggest what language/technology is easiest to do this in or with?
You can use any language out there to accomplish this and many other tasks. It's really about preference and what one's you know best. You can use Perl, PHP, Python, Ruby, C, C++, shell scripts (sh, ksh, etc.), and so on.
It should be easy to do in Perl, with LWP:imple & HTML::TreeBuilder.
Then again, is the data you want to pull in a table? The Windows version of Excel has a pretty nice feature that let's your grab external web data. From there you can use whatever other features you want (e.g., pivot tables, charts, etc.).