I'm a big fx junkie. Been doing guitar pedalboards since long before any of these companies started to make products that you can actually use on a pre-fab board... hell... even before pre fab boards.
I also have experimented with fx for vocals. I've tried the cheap digitech multi fx shit, the expensive versions by TC Helicon, and even a handful of extra gtr pedals I had sitting around.
The all-in-one, extra tweakable stuff is nice if you don't have a job and can sit around all day trying to come up with good sounds. BUT... they will inevitably sound different when you get to each venue. They also limit the order of fx you can use, and also how many you can use at once. I think this rule applies to the expensive digital units. The cheap ones just plain old suck, and feed back like crazy. Not to mention that they are even MORE limited.
What I have found interesting is that recently, TC Helicon started making individual pedals for vocals, with what looks like some linking cable to make life easier. They are singular fx that you can make a vocal pedal board with. I'm very much thinking about getting a bunch of those.
Now you say, "canned" fx pedals... What you DO get with those is quality vocal fx that are specifically tuned for use with mics (not instruments), and you can put them in any order you want, and turn them all on at the same time, if that's what floats your boat. And the best part is that each pedal is individually tweakable... with knobs... that you can see, rather than a virtual menu that is not shown while in use.
To recap:
Crappy
http://www.musiciansfriend.com/pro-audio/digitech-vocal-300-vocal-effects-processorBetter, but still crappy... and too expensive for what you'll get
http://www.musiciansfriend.com/pro-audio/tc-helicon-voicelive-2-floor-based-vocal-processorAwesome...It's about damn time!
http://www.musiciansfriend.com/search/search.jsp?sB=r&question=TC+Helicon+VoiceTone+Singles