What's your favourite 'cheap' accessory.

With Christmas coming up, I thought it might be fun/useful to see what low cost accessories you have that you use and like.

I know that nobody in my family will be surprising me with a 300 2.8 under the tree, so maybe I'll see some alternatives here.  

I use these fairly often - there's a few people selling them on eBay:
A cheap, compact flash diffuser that works nicely on a SB-800. 
http://www.ebay.com/itm/NEW-SALE-Flash-Diffuser-Soft-Box-For-Nikon-D90-D80-D70S-D60-D40-Z091-/321032264041?pt=Camera_Flash_Accessories&hash=item4abf039969

I love my Eneloop batteries!
http://www.thomasdistributing.com/NEWEST-VERSIONSANYO-ENELOOP-AA-NIMH-Rechargeable-Batteries-4-Pk_p_21.html