Jeanne Tripplehorn and Paget Brewster, Criminal Minds

Tripplehorn has yet to debut as Alex Blake, but since she pulls double duty as a linguistic professor, we expect her to be an ambitious and tough new presence in the BAU. Lest we forget, Brewster was also a replacement, joining the procedural in Season 2 after original cast member Lola Glaudini left. But Brewster's dry, oft-mysterious Emily Prentiss became a fan favorite and had many yearning for a Hotch-Prentiss hookup. (Don't worry, Alex will have a longtime boyfriend.)