The correct version is with regard to. In summary:
With regard to
With regards to
In regard to
In regards to
Note: Even though with regards to is getting more popular, it should still be considered an error. (There is more on this below.)
With Regard To or With Regards To?
Writers are often unsure whether to write regard or regards in phrases like with regard to and in regard to. The correct versions are:
With regard to…
In regard to…
"With regard to" is getting more popular but should still be considered an error
The phrase with regards to has been growing more popular since the 1990s, but it should still be considered an error. The graph below (from Google's Ngram Viewer) compares the uses of with regard to and with regards to in literature since 1940.
There are good alternatives to "with regard to" and "in regard to"
Many people consider the phrases with regard to and in regard to as cumbersome business-speak.
Of note, the phrases with regard to and in regard to can often be replaced with a shorter alternative. For example:
We need to talk with regard to your request.
We need to talk about your request.
I have received your complaint with regard to the noise.
I have received your complaint regarding the noise.
With regard to your request, we will consider the payment on Friday.
Concerning your request, we will consider the payment on Friday.