If we're talking about boosting the mount's power in any way possible, as opposed to expressly boosting paladin level wrt special abilities, then I'd also recommend the Warbeast template, from MMII, if the DM will allow it.Jubilee said:There's also Celestial Mount, found in book of exalted deeds, which basically applies the celestial template to a paladin's mount (pre-req is paladin lvl 4).

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.