Looking through the posts here, I can safely say that there seems to be three schools of thought about the summoner...
-The Eidolon is the purpose of this class, the humanoid with the spells is secondary.
-The Eidolon gets too much power and there needs to be a larger focus on actually summoning things.
-Summoner is overpowered.
It seems to me there's a pretty clean split between the two things the summoner does:
A) Have and buff an Eidolon
B) Summon random monsters to throw at people.
One issue here is that the Eidolon, as cool as it is, is not flavored like a Summoned Monster, but like an Animal Companion. It takes 10 rounds to summon, making it impossible to call in combat, and can only be summoned once per day. Dismissing it and re-summoning regularly is entirely out of the question. Allowing it to be regularly called and dismissed, perhaps that 3+Cha times per day, for a limited duration, would help increase the thought of "I am an awesome summoner" and decrease the idea of "We no longer need a fighter." Doing this could, in fact, justify giving the Eidolon MORE power, as it will cost the summoner at least a standard to summon it, and it will not have to worry about serious reprocussions from running out of hit points.
On the other hand, some people just want to have a really cool monster all the time, and there's plenty of reason to want that: In 4E, the best part of being a Druid is that you can just be a bear all the time if you really want to. So how do we reconcile the two opposing schools? The same way Rangers, Wizards, Sorcerers, and so many other classes do: Choose a specialization.
I propose allowing the Summoner to pick either Eidolon Specialization, Summoning Specialization, or neither specialization.
Eidolon Specialization would have a constant Eidolon, as presently designed, but the Summoner would exchange it's 3+Cha summons per day for a buff-oriented spell list. Certain spells, such as Fly, would be avaliable 1 level lower with the stipulation "This spell may only be cast on your Eidolon." Other useful buff and support spells, such as the Cure spells, would be added to this Summoner's spell list, with the target line replaced with "Target: Your Eidolon."
The Summoning Specialization would have an Eidolon that had to be called with a Summon spell, and would not be around constantly. This summoner would also lose features like Aspect and Shield Ally that rely on the Eidolon. Insted, the Summoner would gain the Conjurer's ability to increase the duration of summon spells, the Abyssal Sorcerer's ability to gain bonus summons and to grant summons DR (though not necesarrily alignment DR), the Augment Summoning feat as a bonus feat, and other such abilities to enhance the power of summon monster spells. This summoner would have more power per encounter, as most spellcasters do, but would not have the Eidolon Specialization's benefit of being able to have an awesome monster all day.
In the middle would be the split focus summoner, similar to the class as is now, though with a weakened Eidolon and a few more bonuses to casting (there's really no reason for a class called Summmoner to not get Augment Summoning as a bonus feat).
Alternatively, these features could be chosen at various levels. At level 1, for example, you could choose to trade your 3+Cha summons a day for an Eidolon-happy spell list or you could choose to trade your permanent Eidolon for a stronger Eidolon that costs your Summons spells to bring out. At level 4, when you would get Shield Ally, you can choose to trade that in for Augment Summoning, etc, etc.
The simple point is, there seems to be a clear split between people who want to throw a giant monster at their foes and people who want to show up Conjurers and Abyssal Sorcerers, and a lack of an option to focus one way or another will only result in this class being overlooked too often in favor of Druids (who have the buff spells to make their companions crazy and can turn into monsters themselves) and Conjurers (who can summon armies more effectively and compliment it with a better spell selection... And can use spells to turn into monsters themselves, if they really want to)
