We used Seaside Celebrations for all our rental needs during the wedding ceremony and to supplement what our venue couldn't provide during the reception. I can't say enough good things about this company. For our beach ceremony (at the Edgartown Lighthouse) they provided a chuppa, chairs, several tables, a lectern with audio (and standing mic) for clergy and a speaker system with ipod dock for the processional music. For the reception, on the grounds of the Harbor View Hotel, they provided a tent (with gorgeous decorative & functional lighting), heaters and some tables (we used a variety of table sizes in the dining tent to get the most out of our space, Seaside had the 60" tables the hotel didn't).
Seaside has done set-ups at the HVH and lighthouse countless times and I trusted their judgment and suggestions completely (but when I did have set-up ideas of my own, they were perfectly willing to work on them), and was not disappointed with the end result. Easy to work with, the quality of the rental items was fantastic, and both the ceremony set-up and tent were visually stunning. I was amazed. They're also really nice. I should also note that their prices were far more affordable than many of the other rental companies on the island.