I think he's looking more for an actual harmonizer pedal. Can't say I've ever tried one that was worth using, but I haven't checked out any new equipment in the last few years. I'm sure all the main manufacturers like Boss etc.. must have em listen on their websites if they have them. The only way you're going to really know if it's good enough for your own playing is to actually test one out.
Personally I've always found other ways to achieve the same effect like the delay pedal thing or just getting your drummer to play to a click track and record the audio parts in a sequencer or use a midi file with a guitar simulation sound.
The main problem with harmonizer pedals is they always harmonize by a specific amount like 1/5th etc..
and whenever a guy gets one he feels like it has to be used in every song.
It's kind of like wah pedals. They should only be used sparingly to improve a solo rather than using them to show off. It's better to be known for your playing than the nifty pedals you use.
How's that for a whole bunch of unwanted advice :)