Under the "Unearthed Arcana" section The SRD has an option for Conjuration focused wizards where they can give up a familiar in exchange for making Summon Monster spells 1 standard action, rather than a full round action. You might want to talk to your DM about something similar (perhaps giving up an animal companion).
Sounds like a fair trade. The same book lets a Wiz/Sorc trade a familiar for a Ranger animal companion, which means half level progression. You''d be trading full familiar progression for a "familiar equivalent" feature. That added "loss" can be argued to make up for the fact you weren't required to specialize in something like a conjuror is, if the DM tries to make that argument.
Far as spellcasting goes, while Druids are a very strong class, possibly the strongest, in terms of spells alone, their list is absolutely the weakest of the four primary casters. If it's core only, I suppose you could argue that sorcerers are worse off due to spells known limits, but once you introduce splat books, you get a whole slew of sorcerer only spells that (IMHO) do more than "re-balance" the sorcerer. Particularly, Wings of Cover and Wings of Flurry (Races of the Dragon). In a straight out caster duel, the druid will lose if the other caster can avoid melee and grappling. Druids simply don't get the useful abjurations like dimensional anchor/lock, and recieve others at higher spell levels, like greater dispel magic. The utter lack of teleportation (beyond some things like tree stride) and plane shifting is also problematic. Druid spellcasting is also very reliant on the surroundings. For example, Entangle is a very good spell, but it can only be used in certain locations.
From my experience though, I've found Druid casting to be the very best when it comes to "bullying" non-casters. The combination of healing and blasting options, as well as fairly easy access to flight (Wildshape, Master Air spell is only level 2...) is strong on a standard Fighter or Rogue. And Druids have almost as many battlefield control options as a Wizard, especially with Splatbooks. In particular, a Druid can automatically defeat any foes limited to the ground, even entire armies. Entangle, Briar Web, Spike Stones... these all have very large areas of effect. With my last Druid, I focused on getting enemies into as many grapples and entangles as possible, throwing out Entangle, Kelpstrand (eventually many strands with amazingly high grapple check -- read it carefully and see), Spiritjaws (like spiritual weapon, but can grapple and pin), and buffing with Entangling Staff (swift action to cast, every hit lets you try and grapple/entangle the foe). The last three being in Spell Compendium. With the proper layout of control spells, you can really just sit back and let your summons and companion finish things off.
Here's some of the PH control spells of note:
Spike Stones :: d20srd.org
Spike Growth :: d20srd.org
Note with both, unless you can make a high level search check and have trapfinding, you can't even tell where the spikes are! Plant this around a large group/army, and unless they have DR, you've now killed them all or forced them to stay put while you lay down some more spells from range.
Some more useful low level Druid spells from SpC:
Lesser Vigor - better yet, get a wand of it. Much more efficient out of combat healing than what else you have.
Blinding Spittle - Arguably, w/o a spellcraft check, the target shouldn't know it can be removed with water. Even if the DM rules it common sense, many monsters you encounter don't have the luxury of reaching in their pack for a waterskin. Level 2 Blindness spell with no save!
Crab Walk - Good boost for party's melee charger or your companion
Enrage Animal - Does as you'd expect; no fatigue afterwards
Snake's Swiftness, Mass - Basically lets all allies make an immediate melee attack. Useful with lots of summoned allies, and you get it earlier than a Wizard
Listening Lorecall - Level 2 and 10 min/level, with listen ranks gives blindsense/blindsight.
Blood Frenzy - If you've got a barbarian ally, or take the Avenger Druid variant. Basically grants a free use of the Rage class feature.
Girallon's Blessing - Long lasting and gives extra pair of arms, always good.
And again, Kelpstrand, Master Air, Briar Web, and Spirit Jaws are all amazing.
