In (non-EE) BG2, Ranger/Clerics get 2 significant advantages that neither class has individually.
1. Ranger/Clerics can use *all* Druid spells (other than HLAs) that their Cleric level is high enough to use. This means that, at Cleric level 9, Ironskins can be used. Also, it means you get 7th level druid spells before a Fighter/Druid would. (Note that, for dual-class Ranger->Cleric, the character's Cleric level must be higher than her Ranger level for this to apply.)
2. A multi-class Ranger/Cleric starts learning HLAs early, at 2.25 million total XP, instead of the usual 3 million. This means that you can get HLAs such as Whirlwind Attack and Deathblow significantly earlier than you would otherwise be able to. This does not get you more HLAs in the long run, as you get them only at Cleric level ups until late. (Note that your first HLA can't be a cleric one, as your first HLA comes before you get access to 7th level cleric spells.)
Also, don't forget that the Flail of Ages exists, as does one weapon that gives its wielder 25 Strength; both are usable by Ranger/Clerics.
Fighter/Druids do have one significant (though temporary advantages); they get 6th level spells (including Heal) before even a single class Cleric does. Also, at 6 million total XP, they get more 7th level spells. (The downside, of course, is that they don't get any Druid levels from 3 million until 6 million.)
I can't confirm this, but I've read that the engine lets ranger/clerics use their cleric spell slots for ranger spells. As ranger spells are often unique to the class, and more powerful than other spells of that level (because you normally only get them later) this gives you more powerful low level spells than a normal cleric would have. As I said, though, I haven't tested this and might be completely wrong.
Actually, Ranger spells are not unique; they are just the spells a Druid gets, but learned later. Note that, for Ranger/Cleric, the "learned later" part does not apply, and the spells do indeed share slots with Cleric spells.