Detect Favored Enemy, Rgr 1, SpC - like detect magic, but on FE
Exacting Shot, Rgr 2, SpC - 1 min/level, ranged weapon auto-confirms crits on FE's
Foebane, Rgr 4, SpC - 1 round/level, Weapon becomes +5, and +2d6 damage vs one selected FE (also +4 Resistance to saves vs FE)
Mark of the Hunter, Rgr 3, SpC - 1 min/level, vs one creature (who must be a FE), your FE bonus increases by 4, subject cannot gain cover or concealment other than total
Bane Bow, Rgr 4, Comp Div - 1 round per level, ranged weapon becomes +5, and gains the Bane property against one of your favored enemies (effectively +7, +2d6 damage).
Hunting weapon property, MIC, +1, increases your FE bonus damage by 4 (all FE's)
Originally the Raptor Arrow relic from Complete Divine gained the bane property against a ranger's favored enemies. As of MIC, they gain the bane property for anyone, against any creature type, so long as you have created the proper divine connection. The CD versions were also +3, while the MIC ones are merely +1.
The Abolisher PrC from Lords of Madness grants FE Aberrations (and limited wildshape)
Ascetic Hunter feat allows your FE bonus to increase the DC of Stunning Fist