In case Zachiel hasn't made it clear enough...

These Are Mainly Examples

Excludes corner cases.

• The cleric, druid, wizard, and other casters who prepare spells must prepare spells that're to be modified by one or more metamagic feats, designating each spell to be affected by the metamagic feat when the spell is prepared. The spell occupies a single spell slot with a level equal to the spell plus additional levels equal to all the metamagic modifiers. Casting time is unaffected unless a byproduct of the applied metamagic feat.

  • Example 1: The 1st-level Clr spell divine favor [evoc] (PH 224) modified by the metamagic feat Extend Spell (PH 94) occupies a 2nd-level spell slot. A cleric must be at least level 3 to prepare such a spell.
  • Example 2: The 1st-level Wiz spell color spray [illus] (PH 210) modified by the metamagic feats Silent Spell (PH 100) and Still Spell (PH 101) occupies a 3rd-level spell slot. A wizard must be at least level 5 to cast such a spell.
  • Example 3: The 4th-level Drd spell blight [necro] (PH 206) modified by metamagic feats Empower Spell (PH 93) and Maximize Spell (PH 97-8) occupies a 9th-level spell slot. A druid must be at least level 17 to cast such a spell.

• The sorcerer, bard, and others who cast spells without preparation (including a cleric or druid using the class feature spontaneous casting) can choose to apply one or more metamagic feats they know to spell they are about to cast; this either increases the casting time for spells with a standard action casting time to a full round or adds 1 full round to the casting time of spells with longer casting times. Further, the metamagic modification changes the level of the spell slot used when the spell is cast to a spell slot of the spell's level plus that of the metamagic feat's modifiers.

  • Example 1: A bard has a spell known the 5th-level Brd spell song of discord [ench] (PH 281) as a spell known and possesses the feat Still Spell (PH 101). He can either cast the spell song of discord as a standard action as a 5th-level spell or cast the spell song of discord modified by the feat Still Spell as a full-round action as a 6th-level spell.
  • Example 2: A sorcerer has as a spell known the 7th-level Sor spell summon monster VII [conj] (PH 287) and possesses the feat Empower Spell (PH 93). He can either cast the spell summon monster VII as a 1-round action as a 7th-level spell or cast the spell summon monster VII modified by the feat Empower Spell as a full-round action followed by a 1-round action as a 9th-level spell.
  • Example 3: A cleric who has metamagic feat Maximize Spell (PH 97-8) hasn't prepared the 1st-level Clr spell cure light wounds [conj] (PH 215-6). The cleric wants to use his spontaneous casting class feature to cast the spell cure light wounds and modify the spell with the metamagic feat Maximize Spell (PH 97-8). Because cure light wounds normally takes 1 standard action to cast, it instead take a full-round action to cast. The spell cure light wounds is normally a 1st-level spell but the feat Maximize spell makes the spell use a 4th-level spell slot instead.

No, your assumption that rituals do not have to be prepared is wrong.

You can cast a cleric spell as a ritual if that spell has the ritual tag and you have the spell prepared.

You might be thinking of wizards, who don't have to prepare rituals, but that's because their ritual spellcasting explicitly says so:

You can cast a wizard spell as a ritual if that spell has the ritual tag and you have the spell in your spellbook. You don’t need to have the spell prepared.