The "experts" seem to be in agreement that it's better to have different sexed dogs in the same house despite the fact that many YT'ers have had good experiences with same-sex dogs.
Fran's article from veterinarypartner.com was a good one. Here is another from the same site. (The whole site is excellent, BTW, for those of you who haven't found it yet).
http://www.veterinarypartner.com/Con...=883&SourceID=
Most sources will tell you that these combinations go from best to worst:
male/female mix
2 males
2 females
Good luck!