Wow Bingo, impatient much?

I can't speak for others but with the show no longer being on air, I don't frequent here as much as I use to so really, expecting an answer 4 minutes after you posted the thread is asking a bit much.
For me, personally, I always prefer finishing a fic before sending it off to my beta reader. Some people are different. I would even hazard a guess that it's something that's between the author and their beta reader.
I personally am not interested in being a beta reader as my grasp of the English language isn't as good as it should be. I know that if you use fanfiction.net they have it set up so you can search for a beta reader.
There is also a newish (at least to me) fan fiction site to post works on (sadly they have NO TLW works up yet - I plan on adding mine to the collection).
http://archiveofourown.org/ - Archive of Our Own (AO3). It's a beta site and they do have a waiting list to be allowed to post fics. It took me about 4 days to get accepted. It's fairly easy to navigate and doesn't have any adds like ff.net has.