Many of your male clients are undoubtedly family men. After they are done putting in hard hours at the office, they go home and engage in a job that is equally as much work and requires even more emotional investment. Show your recognition for their commitments outside the workplace with Father's Day-themed promo items.
Give your clients custom coffee mugs that say "Number One Dad" or the traditional "Happy Father's Day". They will appreciate the sentiment and will be able to realize their greatest accomplishments – their children – every morning as they sip their coffee.
You can issue other gifts that demonstrate your propensity for family appreciation, but are also practical in the workplace, such as business pens. Have your company name or logo inscribed and then under it wish them a happy Father's Day. A businessman knows one can never have too many pens, especially when note taking during client phone calls plays a large role in their jobs. They will be grateful for the pragmatism and the consideration.
For a more traditional touch, you can always send out promotional holiday cards. The thought alone is enough to warm your client's heart.