I'm going to keep this to names only in the interest of minimizing spoilers.
#Key
#: Only availiable as a continued romance if initiated in Mass Effect 2
^: Same Sex Romance option
%: Not a Squad Member
$: Confirmed as Counts for Paramour
#Male Shepard
Ashley $
Liara $
Tali #$
Miranda #%$
Steve Cortez ^%$
Kaidan ^$
Diana Allers %
#Female Shepard
Kaidan $
Liara ^$
Garrus #$
Samantha Traynor ^%$
Diana Allers ^%