CBS.com is doing something really cool this year -- they're making certain episodes available for viewing online through their new InnerTube program. Right now, Brutus, Waste Not, Hardball and Provenance are available. Numb3rs isn't the only show they're doing online either. NBC is doing something similar with their Rewind.
There aren't a lot of legal ways to do it, and that's one of the few. Sometimes iTunes will offer episodes for download (which is also legal, as it is sanctioned by the networks), but I'm not sure if it has Numb3rs.
abc is also doing that with some of there shows, but i think CBS started watching the entire episode online thing