This will vary from area to area and the task/expertise of the consultant. Here (RTP North Carolina), the rates tend to run from about $75-$250/hr. The median is probably $125-$150...
Of course more basic tasks go for less and specialized skills or urgent response goes for more. I traditionally work for a standard fee, but offer "support options" where the rate is reduced for "regular" customers. This works well...but make sure you are consistent. Otherwise you can end up with some very irate customers.....
Good luck. Hope this helps (and I look forward to seeing the other responses here).