One of the best ways to watch an SPN episode is to just download it. If you've got a good site then it's good picture and the sound is in synch with the rest of the video unlike most sites where you can watch it online. A good free site for downloading is
link I use it myself and it works great for me.
You can also watch it online if you don't want to or can't download it. Some good sites ypu can try are
link ,
link and
link
or you can just look on fanpop, when a new episode airs there'll probably be a video and some links to it in the video and links sections.
And I'm not entirely sure but if you live in te US you can probably watch it on the CW site or on Hulu.
There are plenty of things you can try, have fun watching :)