The first template is often-maligned Celestial, best known for providing wizards with expendable summons. The tier system for templates lists it as 'tier 5': literally the lowest of the low. I don't completely agree with the rating, but it illustrates how little Celestial adds to your character for +2 LA.
What does it give you? Darkvision, weak spell resistance (an equally-leveled caster will penetrate it 75% of the time), a weaker version of Smite Evil, usable once a day, and scaling energy resistance and damage reduction. Oh, and if you're an animal or vermin you become a sentient magical beast instead, which is a negligible benefit unless you're looking for a cheap way to make your vermin PC playable.
The scaling abilities slightly complicate picking an appropriate LA. If you only have a few HD, you gain nothing but a few uncommon resistances. You then gain DR/magic, which is briefly useful before becoming near-worthless due to enemies with magical gear getting more common. The subsequent increases to both of these abilities don't add much to their overall use.
All things considered, I can't really put this at anything other than +1 LA. At +0, it's simply too strong not to take, whereas +2 would keep it terribly underpowered.