For a long time I resisted putting reverb on vocals when mixing live. It was a philosophy created out of mixing on an adequate system in sub par rooms (or terrible systems in terrible rooms). Every time I dialed up reverb things would just get muddy and indistinct. Some nights I had to turn it up so far just to hear it that it started to sound like the singer was in a bank vault. So I skipped it and saved the reverb to put a little edge on the drums.
Instead I'd reach for a tap delay, usually with enough feedback to give me about two repeats. While feedback is usually a dirty word, for those not familiar with the inner workings of a delay unit, it's the parameter that feeds a percentage of the effect back to the input and gives you second, lighter echo. 30% or so will give you a second tap, 60% makes it about three.
My technique varied by the song and the group. A band playing oldies might get a real short (120 milliseconds) tap with no feedback for that "Buddy Holly" slap back sound. Push it up and it sounds very affected or just float it in there a little to thicken things up a bit. More often than not it was cover bands playing more modern rock. Sometimes I would think back to listening to the radio and manage the delay to match a particular song. Other times I would just match the tap tempo to the song.
The real key when using longer delays was one, getting the timing right and two, not laying it on with too heavy a hand. Ideally you would only hear the effect at the end of a line. It makes a vocal sound more powerful, like it's echoing off the majestic hills. (It's also been the butt of many a joke, even in song. "Don't forget the delay-ay-ay, on the very last word-ord-ord".) As for the timing, I found that if I matched the tempo of the song exactly then the repeats would get in the way of the next words. I would usually tap in a time for a song during the intro, then roll it up a few dozen milliseconds. More modern boxes than what I had back then will let you do things with dotted notes and that's sort of what I was trying to achieve.
One additional trick that I like to keep on tap (pun intended) is to absolutely slam the return channel on a long, held out note. You have to time it right, when you push it up and when you take it back out. In this instance you don't want a ton of echo after the note but some build up during it will make it sound huge (as long as the singer is in tune). This works great on genres that have a lot of screaming. Push it up as the scream starts and take it back off just as they finish and the band will have that little extra something that puts them head and shoulders above the rest of the angst ridden masses.
Now days, even on a good system in a good room, while I do use a touch of vocal reverb (plate, because it doesn't get in the way too much) I'm still reaching for the delay on every song. I tweak and manage it to create some space. I back it off when the vocals get thick and lay it back on strong at critical moments. Sometimes my finger never leaves the return fader.
That's my two cents on vocal effects Brethren of the Knob and Fader. What tricks are you up to?