Write up a press release and send it to local media outlets, including newspapers, tv stations and radio stations. You never know when they will do a quick mention of your company or event, and the effects could be grand! Don't forget local bloggers as well, they are usually wonderful to work with and can have way more reach than you ever would imagine!
See if your community offers any groups such as the chamber of commerce or small business association. They can usually help if you are having a grand opening or ribbon cutting ceremony, and these people usually have connections with local big wigs and celebrities that you would want at your event! If you are a small company, you might want to consider co-hosting an event with another company. That way you can invite twice the customers!
Don't forget social media! Twitter is a great way to spread the word about events in your company! Don't forget the all important "hashtag"! You can also create an event on Facebook and invite your fans. They can, in turn, share with other fans, and increase your attendance. Don't forget to send out invitations to your email contacts, and your current and past customers whose addresses are available to you.
Don't forget some of the age old ways of attracting people to your event. Advertise locally if you have the budget. Signage, and balloons, etc. are always a good thing! Word of mouth is still the most powerful advertising medium, so tell everyone you see about what is going on, and ask them to tell their friends! Offer an incentive to customers who attend your event: free refreshments, raffles, prize giveaways, etc. are all great ways to draw in the crowds!