I was going to write this big long thing about why I think you should read these fics, but then I decided that they are both so good that I couldn't do them justice in that way. They speak for themselves.
Yours, Mine, and... Nevermind by
lionessvalenti (Jack/Ianto, PG-13, 1,890 words)
Season of Grace (Coming out of the Void) by
nancybrown (Jack/Ianto/Lisa, Alice/Johnson, PG-15, 19,000 words, Spoilers for CoE)
Just... read them.