I have a 15 Ranger/4 Rogue/1 Cleric that works well because the Cleric level boosts the Ranger abilities by:
1) Giving me a free Cure Light Wounds that is boosted by my Ranger Healing Amp. (good for cheap top-offs) and opens up a Ranger spell slot.
2) Raising my Will save.
3) Giving me 160 additional spell points (I'm at 651 with my SP item).
4) Giving a few useful spells like Nightshield, Divine Favor, Obscuring Mist and Remove Fear.
5) Some useful wand and scroll use.
I took it because nothing else added so much for so little (except Monk, which I don't own) and neither one more level of Rogue nor Ranger would have given much either. Definitely not a build for everyone though.