I've bought the Sony polarising filter set, which makes a difference to outside footage on bright days and the 91D battery.
I'm thinking about buying a Rode VideoMic as the onboard mic is only adequate for close range shooting. However I'm trying to work out the best way to connect the Rode VideoMic to the HC1E or my tripod.
I've just bought a Manfrotto Car Pod so I can connect the HC1E to windows on steam trains. Yes, I take footage of trains

This is much better than hand holding the camcorder when a tripod can't be used.
The 0.7x Sony Wide Angle lens is probably next on the list along with the Mic. I'll have to wait for the credit card bill to roll over to next month as I also bought a Manfrotto tripod at the same time.
Over the moon with the HC1E, footage is fantastic.
For the moment I edit using Pinnacle Liquid 6.1 and play directly back into the plasma. I was thinking of buying a Snazzio Media player to play the edited high def MPEG2 files but I've decided to buy more camcorder accessories instead and wait for HD-DVD or Blue Ray players to arrive and do the job properly.
One thing which surprised me, I use the manual features more than the auto settings on the HC1E. The manual zoom is great, much greater control. I'm glad I went for the HC1E now.