Selling off some games (again)

I keep saying I want to get rid of some of my games, but being the worlds greatest horder it never happens. My shelfs are getting full though, and I'm seriously not playing half of this shit, so today I listed all of my games at home and did a first pass of what I may try and sell off. Here is the list:

• Age of Mythology
• Amun-Ra
• Battlelore (+ call 2 arms and promo figs)
• Betrayal on house on the Hill (whats this worth???)
• Cleopatra and the society
• Delta V
• Dungeon Twister
• Incognito the Card Game
• LOTR- the Duel
• Lost Cities (yuk!)
• Maharaja
• Modern Art
• Odins Ravens
• Purto Rico (+ expansion)
• Return of the Heroes (+ dragon expansion)
• Princes of Florence
• Through the Desert
• Ticket to Ride Europe

 Maybe list

• Battleball
• Quest for the Dragonlords (+ crystal of power) [never played this]
• Risk 2210 AD [never played this]
• Roborally

How do you guys normally work out an asking price? 50% of retail?

This is all so strange to me.