Well, the most expensive cels would be, of 
course, Raphael. And then, Miruru can go for 
ludicrously high prices...I chalk it up to the 
catgirl-fetish that is so predominant. Good shots 
of Silky can also go for very high, because she 
just oozes that Rei Ayanami indifference that 
Japanese fans love.

Gabriel cels go very quickly, as well, since he 
is a fan favorite among girls (as is the case 
with many Kanna Nobutoshi characters...Tasuki, 
anyone?). Ruka cels go for cheap, but if you find 
really god cels of her they can get up to about 
$50-75. Good Noelle cels can get pretty pricey 
too, especially if she's with Yuusuke and 
glomping him...people love those. Good shots of 
Sara always go far too quickly (what's left is 
always ones of her just looking wierd in some 
way). So if you find a great Sara cel, nab it. 
Good cels of Mama can actually get pretty pricey 
as well. Mikael is also a fan favorite, for his 
relationship with Rphael as well as his "cool" 
attitude in the fist half of the series (and 
again, popular seiyuu here...Ishida Akira, AKA 
Xellos...)

Also extremely pricey are cels from the last ep 
of:

S
P
O
I
L
E
R

Anyone (being Noelle, Mikael, or Silky) with 
wings. Or of Mikael looking decisively evil. 
Those tend to go very high.

S
P
A
C
E

E
N
D
 
HOWEVER, cels from Tennimon also have the 
possibility of going for very cheap, if you're 
lucky. In the past month, I've seen Tennimon cel 
prices skyrocket, due to it's imminant release in 
America. So don't expect them to get any cheaper.

OH! BTW, I got in some cels from the Anime Chaos 
sale today, so I'm updating my Tennimon gallery 
as we speak...mosey on over and check it out! ^_^ 
Posted below is one of the new cels I just got 
in...isn't Noelle kawaii =^.^=

-Misha-chan