Hello
All now prefer buysellads rather than adsense as in buysellads there is no difficulty but the approval of it is somewhat difficult.
So I would say you to try http://www.advertisespace.com
It is very easy to get an approval.
Of course I agree buysellads is the best but if u dont get it approved you can try http://www.advertisespace.com
 As always there are other options too
If you don't like advertiser space you can try puxee.com
I would say it is the toughest competitor for buysellads
So please comment if you found this useful.