Prestige Class Help, Please

[Chanteur]

So for a character I was developing, I am trying to find a prestige class to take the first two levels of. The character will be a LG Cleric 2/Wizard 3/Beastmaster 1 (race not certain), and I'm looking for a class that progresses arcane spellcasting both levels while having prerequisites that don't involve a BAB of +4, and while hopefully providing useful class abilities (the character is a different version of the Ubermount build). I would appreciate any input given. Thank you.

[Flickerdart]

You will have incredible difficulty qualifying for arcane caster PrCs with only 2nd level spells. At this point you're probably better off with another Cleric level and then a level in Mystic Theurge.

[Hirax]

Unseen Seer only has skill requirements, they might be a bit cumbersome for you though. If you're able to visit the Frog God's Fane for a free skill focus to any knowledge skill, Divine Oracle can advance either arcane or divine casting.

[Biffoniacus_Furiou]

Just off the top of my head, we have:
Master Specialist in Complete Mage.
Ruathar in Races of the Wild.
Divine Oracle in Complete Divine, say you visited the Frog God's Fane in Complete Scoundrel to get its Skill Focus prerequisite without spending a feat on it.