Ed's wood stems are great, as Stickstones mentioned. It's nice having a stem you don't have to baby, although I do find that the glass stems deliver denser vapor. I recommend getting a PVHES turbo in either GonG or standard if you want to go all out, as they really do take the Solo's performance up a notch. Arizer should really start doing some of the PVHES-style upgrades on their stock stems, imo.
I have the stealth adapter and don't like it. It comes to too tight a constriction and airflow is really hampered. The Solo is already very stealth with a wood stem or even a clean glass one if you just place it in a travel coffee mug which conceals the Solo's body. Hot cup o' vapor with no extra purchases.
The little black plastic caps are great for keeping a packed stem on the go.