The code "THNX15" will get you 15% off until 12/23.

$70 waterproof bike handlebar mount flex case (the n810 fits nicely inside)
http://www.semsons.com/raramharamof6.html

$20 GPS: http://www.semsons.com/amabg108blgp.html

My favorite (10hz w/o WAAS/SBAS, 5Hz with):

$55 http://www.semsons.com/wigiwblgpsre.html

And there are others which might be interesting - QStarz has a keychain (-165db, switchable 5Hz) BT GPS, a keychain BT GPS + logger, and a 40+ hour, switchable 5Hz -165db GPS.

http://www.semsons.com/qsbtnakeblgp.html
http://www.semsons.com/qsbtnakeblgp1.html
http://www.semsons.com/qsbtblgpsre6.html

And they have lots more accessories and interesting things.

Put your sd card in a CF adapter:
http://www.semsons.com/usbmemcarrea.html
Camera stuff:
http://www.semsons.com/cambat.html