When I was looking at ways to improve the number of spells/day a paladin can cast, I found the Dracolyte prestige class from Draconomicon. D8, full divine casting, two good saves, and rather uninteresting special abilities, with one big exception (ok, the ability to summon a draggon at level 10 may be nice as well): at first level, you get one of 2 'prestige domains', based on alignment, either glory or domination. The special abilities aren't very special (stronger turning check and spell focus (enchantment), the spell list are ok...
but the catch is: "if the prestige domain is the characters only domain, he gains the ability to cast a domain spell of each spell level to which he has access once per day, in addition to those spells he already casts".
Effectively: a 1 level dip in dracolyte gives classes like archivist, favoured soul, paladin and ranger an extra spell / day of each level.
Downside: with two sucky feats as prereq (dragonfriend, toughness) it's not really an option for the feat starved paladin, and it only remain "extra spells" as long as you don't have any domain slots (so no contemplative, ordained champion, seeker of the misty isle and church inquisitor).
Still: is this worth it / can this be made worth it?