hey dnl88
these are some of the special effects i like - i'm not going to cover general vocal processing (doubling/plates etc) as these are well covered elsewhere on older posts and some of the guys here are fantastic at offering advice on good vocal sounds.
but for what it's worth.
i know its been a bit overdone now, but i still like the whole lo-fi sparklehorse-y type sound. i found myself using it on a track only the other day.
another very cool technique (if you have a vocalist who can do it) - works best on slowish, dark maybe even goth-type tracks.... two vocal tracks - main vocal quite close, low and intimate; second vocal a bit wilder, far-away-from-source reverb, an octave up from the original and with lots of the bass end taken out. try it - if done properly, it can be the SPOOKIEST effect ever - i git the idea from a track by Marillion called 'Cathedral Wall' and tries a variant on one of my own tracks, and it just sounds fantastic.
i like auto-panning on dance vocals - particularly those sample-type vocals etc
on psychadelic tracks, i've just got into using multi-mode filters to give vocals that sweep in and out of the track. phasers work well too, but filters that have an LFO and sweepable centre frequencies bring lots of movement into a section.
the important thing about any extreme effect is really not to overdo it.
Google under 'Cher+effect bloody everywhere+autotune+talkbox' - i really wouldn't mention that one anywhere - and if it was a subtle way of asking, then good job you hid it!!!! ;-)
autotune CAN be used quite creatively without overdoing and without using it as a correction tool. you can even use it double vocals if pushed.
best thing is to find open minded artists and have fun and experiment. processing vocals is one of the things i find most enjoyable, i love what you can make the human voice do.
ever seen the film 'Fifth Element'? that film features one of my favourite pieces of vocal resampling - it's when the blue diva is doing her performance at the space resort. it's a wonderful piece of music. sounds a bit dated now, but still good for its time.
have fun! let us know how you get on!