Li Shenron
Legend
The 6th level of spells has given me too some problems before, there are many interesting choices but most of them have downsides which aren't nice. (Anyway I have only the SRD for 3.5 suggestions).
4 of the 5 core necromancies and 2 of the 3 divinations have a Gp cost for example
The last necromancy (Eyebite) can dangerously affect your own allies.
The last divination (Analyze Dweomer) is quite a must in 3.5 because it takes a moment to cast and only has a focus. In 3.0 it was not so cheesy, but in 3.5 really it is a no-brainer.
The abjurations are powerful but:
Antimagic Field is centered on you, so bye to your own protections
Globe of Invulnerability has a similar side effect, and it awkwardly doesn't follow you
Repulsion repels your allies as well, and may hamper their tactical movements weirdly
Amongst the others:
Transformation is definitely good, but you won't be able to cast other spells meanwhile
The "mass animal buffs" are nice, but the PCs who need them most already have high enhancement bonuses from items at this level
I don't know what I would suggest. You could just pick a save-or-die like Disintegrate of Flesh to Stone, with the first being definitely better (does damage even on a save, affects everything and more) but only if you have decent ranged attack bonus. Or otherwise another area damage spell like Acid Fog or Chain Lightning.
All in all the 6th level of spells is not an easy one: there are many goodies, but there are pehaps more spells with a gp cost here than any other level.
4 of the 5 core necromancies and 2 of the 3 divinations have a Gp cost for example
The last necromancy (Eyebite) can dangerously affect your own allies.
The last divination (Analyze Dweomer) is quite a must in 3.5 because it takes a moment to cast and only has a focus. In 3.0 it was not so cheesy, but in 3.5 really it is a no-brainer.
The abjurations are powerful but:
Antimagic Field is centered on you, so bye to your own protections
Globe of Invulnerability has a similar side effect, and it awkwardly doesn't follow you
Repulsion repels your allies as well, and may hamper their tactical movements weirdly
Amongst the others:
Transformation is definitely good, but you won't be able to cast other spells meanwhile
The "mass animal buffs" are nice, but the PCs who need them most already have high enhancement bonuses from items at this level
I don't know what I would suggest. You could just pick a save-or-die like Disintegrate of Flesh to Stone, with the first being definitely better (does damage even on a save, affects everything and more) but only if you have decent ranged attack bonus. Or otherwise another area damage spell like Acid Fog or Chain Lightning.
All in all the 6th level of spells is not an easy one: there are many goodies, but there are pehaps more spells with a gp cost here than any other level.