I actually have two different sets of plugins that I use, depending on the stage of the production. Usually, while I'm tracking, composing, trying out new creative ideas, I pretty much throw an iZotope plugin on everything. Alloy, their designated tracking multiplug, includes limited multiband dynamics, an EQ that you probably should should just turn off in favor of Logics, and some cooler and more obscure goodies like transient shaping and a pretty advanced DeEsser. I find it good for bass, acoustic guitars, and occasionally voice. iZotope Ozone, intended for mastering, actually works better as a bus-plugin for submixes (chorals, drums), and often on solo vocal tracks it sounds better than Alloy. Usually I just slap on a preset and take ten minutes adjusting it, and I've got passable sound for the creative process.
I use this technique while composing and exploring broad level mix ideas -- I don't want to be spending hours in the plugin strip yet, but I can't do nothing cause I can't recognize a good idea when every idea sounds like crap.
The other "set" of plugins I use, for the actual production of a creatively finished piece, is not really a set at all. I start from the top pretty much every time, going through a motley, ill-conceived collection of plugs that I've ended up (probably because I'm physically unable to resist even the simplest marketing ploys.) Not much advice I can offer there, since the selection usually varies with the context. I do tend like IK Multimedia's T-Rack3 for Mastering, though.s
I think the two pronged approach is helpful, mostly for one reason. The first set (iZotope, in my case), provides much more overall utility while being less expensive. It's true that if you've got a track going to the chairman of of Virgin, you're going to spend the time and money to get it sounding as mint as you can. But for me, that isn't usually whats going on. I use the cheap stuff more, and its more indispensable to the overall creativity that drives me musically. Going cheap first and expensive later is something most people do anyway, but in this case, you don't have to throw away the cheaper stuff when you upgrade. And you get time to find out what kind of interfaces you like, etc, before dropping ten grand on Waves Complete.
So, sorry about the novel, but my advice is to get a set of cheaper, versatile plugins first, get comfortable with them, and then base your future, pricier decisions on that experience. And of course, get comfy with the Logic Plugins -- they will always be more stable, better documented, and more reliable than their third party competitors.