What is your favorite prime & why?

I am itching for a new lens.  Likely own too many already, but very few primes (actually only one & its a macro).  I have some money to spend before the end of the year, so...  I thought it would help spark-up my photography fun.  If you can take a moment to tell me about your favorite prime & why (what you use it for) maybe it will help me decide (and I would appreciate it).  My current lens list is below.  I currently shoot with a pair of D7000's and a V1 (that will be here in a few days).  I sold my D700 & D3's in anticipation of getting a D800/D800E - but have held off with the AF issue reported (let's not go there though :-)).  I shoot everything for personal enjoyment - love the outdoors (creatures/critters/landscapes).  I used to professionally shoot weddings, and currently professionally shoot some architecture - website below.

• Nikon 14-24
• Nikon 24-70
• Sigma 8-16
• Sigma 150 macro
• Sigma 120-300
• Sigma 1.4x & 2.0x TC's
  
• Tamron 70-300 (for the V1)

Thanks for the input!

Dave

www.architography.biz