Gaining 3rd domian?

[eamon]

You forgot the Divine Oracle PrC, which gives the Oracle domain, which gives +2 caster level for all divination spells.
The Rainbow Servant also gives access to the Good, Air and Law domains as you level in it.
Seeker of the Misty Isle, in addition to the Travel domain you mentioned, also gives the Magic domain at 7th level.
Temple Raider of Olidammara gives access to the Luck domain at level 10

Good points. The Seeker of the Misty Isle costs you a caster level should you progress until the 7th level in it, however. The Rainbow Servant costs many caster levels, and I don't think it's very playable (unless the campaign is extremely forgiving). The Temple raider doesn't even advance normal spellcasting at all, so it's not much more interesting than, say, the Divine Crusader, which effectively grants a domain (although spread out over the class)
The Warpriest grants an extra domain at first PrC level, but costs a caster level.

The Divine Oracle is interesting (esp. the capstone ability, I think, which allows her to always act in the surprise round.).

 

[Dannyalcatraz]

1) If you take levels in Wizard and take the Domain Wizard Alt Class Feature (CompChamp p52), you gain access to domain spells. If you have any Cleric (specifically) levels, you gain full access to the domain.

2) Cloistered Cleric (Unearthed Arcana) adds the Knowledge Domain.

3) The Contemplative PrCl (CompDiv) adds 2 Domains.

4) The OA Shaman starts off with 2 Domains, and adds a 3rd one at higher levels.

Combining those first 3, a multiclassed PC would have full access to 6 Domains.

Combining the Shaman with the Contemplative gets you 5 Domains. If your DM rules that the "Cloistered" option applies to the Shaman class, you'd add Knowledge for a total of 6 Domains. If your DM rules the Domain Wizard ACF applies to Shaman levels as well as Cleric levels, you could gain another Domain, again totalling 6.

If your DM rules in favor of your Shaman in both cases, that brings your total to 7 Domains- 3 for Shaman, 2 for Contemplative, 1 for Domain Wizard, and 1 for Cloistered.