Hoya NXT Plus 43mm UV Filter — Schott B270 Clear Glass with 10-Layer HMC Multi-Coating for 98% Light Transmission, Waterproof Top-Coat, Aluminum Frame - Camera Lens Filter for Sharp, Clear Images

This! I just got my L10 (stoked!) and as soon as I put a protective UV filter on I hated how the regular lens cap fit/looked. Primed a JJC one from Amazon, and to my surprise it not only fits with the filter installed, it rotated and clicked into place surprisingly well. TBD on the quality / ymmv. I am also probably gonna pay the eBay tax to order an OEM Panasonic one from Japan, but this should (hopefully) tide me over in the meantime.