My cleric has some specific ways to aid some players. For example, he will cast darkness & ebon eyes on the party rogue, enabling constant sneak attacks.
Are you playing 3.0 or has the DM house ruled darkness back to being pitch black?
But what can the cleric do to make a TWF ranger more deadly?
Encourage him to multiclass into rogue. Then rinse and repeat the same buffs as the rogue gets.
He gets energy d6's on his +1 weapons, you then use GMW to enhance the weapons. Hell, if the game uses standard advancement rates, a 20th level wand of GMW may have enough charges to make sure everyone has a +5 enhancement in addition to whatever effects their weapons have for a very long time.
IIrC there is a
Bane spell in the Spell compendium.