I just mentioned this on the other thread about "perms vs. hairpieces" but here it is again: I like
www.wigs.com and my favorite brands of synthetic 3/4 and ponytails are: Wig Pro and Rene of Paris. Since your own hair is showing and computer monitors vary, you may want to consider buying a color wheel to check color carefully before ordering - there are restocking fees if you have to return it and some are NOT returnable. I always order #33 Dark Auburn, my hair is sort of that color and my hairdresser colors my hair to match my hairpieces. It's a nice look and very natural; your own hair and hairlines shows so much people really can't tell you are wearing hairpiece.
I'm not sure what "half-wigs" are but 3/4 wigs are classified as "falls" and 1/2 falls are more like very full ponytails.
My tip on ponytails is that the interlocking combs just don't stay - I get the butterfly or claw clips instead. The combs on the 3/4 falls are different; they are at top and bottom and you also pin hairpiece to hair.
Full wigs are just too hot for me, even with mesh top.
Hope this helps!
--Nisima