The groom’s attire should reflect the formality of the bride's wedding gown and the wedding. If you’re in a ball gown he should be in a tuxedo. If you’re getting married on the beach he should be in light slacks and a white button down.
Before shopping for him you should have picked your wedding date, time of day and location and your wedding dress. Just as your wedding gown's style will be dictated by the time of day and the venue or setting, so will the groom's.
Kleinfeld’s new Men’s Department has a great guide to the different formal wear and suiting style for men. You can see it, along with their product selection, at kleinfeldmen.com.