I kinda like the looks of the speakers "in the buff," but attractive grilles are cool too. We used to make grilles available that were made from wicker stretched over a frame, but they were very expensive and so we stopped having them made. Another good idea is to put velcro in the four corners on the front baffle and attach a foam grille - You can cut it to size pretty much anything. Thomas uses the mesh grilles too, and I've always liked that option. Frankly, the most attractive grilles I've seen in a long time are those made by some of the regulars here.Here are a couple good examples:
Jeon's Theater four π's
Garland's Theater four π's
There are a lot of other super attactive π Speakers people have made, some with grilles and some without. One place you can go to see some of them is Danny's π Speaker website.