This post contains spoilers aplenty. So if you don't like spoilers, go away. Now, for the rest of us, let's discuss...
We've been kept in suspense (-ish?) about the woman who would actually want to be with boring ol' Ted (awww, but really), and the answer was revealed in the HIMYM's season 8 finale. The mother of Ted's children is presumably Cristin Milioti — who you might recognize as being a very sexy baby.
Fans of the show might've expected a big name — after all, they've been waiting approximately 300 years to find out who this person is and anyone less than Mahatma Gandhi is kind-of a let down at this point — but series co-creator Craig Thomas says of their choice:
We didn’t want it to be a big famous star because we didn’t want the wider audience to have associations with whatever actress this would be, where it’s like, “Oh, it’s Anne Hathaway and I think blank of Anne Hathaway….” You’re waiting years to meet this woman, and it’s like, “Oh, he’s in love with Amy Adams just like the rest of America is.” The whole idea is that Ted’s never seen this woman before, so it better feel that way to the audience.” Cristin Milioti is a fantastic actress and she’s been in [Broadway musical] Once, and it’s a Tony-nominated, wonderful musical but she hasn’t done a ton of big TV parts or bigger film parts. It seems so much more interesting and so much more ted to find someone special and unique and new, someone that we haven’t seen before and the whole idea is that Ted’s never seen this woman before, so it better feel that way to the audience.
For now, all we REALLY know is that Milioti caught a train to fictional Farhampton and has the yellow umbrella Ted's always yammering on about their mom owning. Oh, and she's rocking some tremendously ugly boots, but I don't think that's crucial to the plot. Season 9, ahoy!