Lots of great posts. I too like a concave tamper, as I really liked the way a golf tee worked, so I made mine in that fashion. I still use tees, because they're so cheap. I also like a scoop, shovel thing on the end to help me clear the chamber when I am done. I don't ever use a pick, because I just don't even need one. But, I also try to make the scoop end not too sharp, because I want to be able to carry it in my pocket.
Also, if I am kicking back with my pipe and focusing on the ritual and the process, I like to have something to look at, a visual catalyst for thinking, so I put really unique stones on mine, opals, spectrolite, stones that look like little shards of magic. Something to gaze into and loose myself in while smoking. But, then again, I love stones. Not everyone is going to appreciate the dancing colors of opals. But, I dig them.