Most pokemon are 50% percent male and 50% male.
Pokemon such as starter pokemon and fossil pokemon are very likely to be male, and will only be female 12% of the time.
Some pokemon are more likely to be found in one gender than another, vulpix and growlithe for example. Growlithe has a one in four chance of being female, while vuplix has a one in four chance of being male.
Some pokemon can only be found in a certain gender, such as Nindoking and Nidoqueen who can only be male and female respectively. Some of these pokemon have a counterpart of the opposite gender.
In addition, most legendaries have no gender, and the few that do cannot breed.
Overall roughly 60% percent of pokemon are equally likely to be male or female, or 70% if you don't include legendaries. Most pokemon that can be caught in the wild at a 50% gender ratio.