Ok I was in the same fix sometime back. But I decided and bought the Nokia 5610. According to me it was the best fone then and will be the best fone for me. I dun need or use the snazzy features some of u ppl might b depending upon. I will try to write down my conclusions for you, its upto you. Believe me I was looking at SE for a good fone but nothing in the 10-13k dept was worth.
I went to the shop for buying a SE but got this phone instead.
So here r my conclusions: -
Nokia
N73 = Symbian (Will get slow after some months of use)
5700 = No twisting parts for me.
5310 = Too flat for me.
6500 = Didn't come out was waiting for this one, thank god got the 5610
Sony Ericsson
W660i = No auto focus
W610i = Weird buttons
W580i = No auto focus (and my boss got this phone)
K810i = Weird buttons
K790i = Almost went for this one but backed out at the last moment, because of the cam shutter protruding out of the back of the phone.
Now its not that the 5610 is a kick ass fone but here are some of its features
EDGE, 3G (none of the sub 12k fones have this), 3.2Mpix cam with autofocus,
OS4 (No symbian

, Dual cam (Didn't know this even after buying the cam),
Cool display, Gives me 6 days of standby time (I dun get calls at all

), dedicated camera button + you dun need to open any shutter or the phone to click
Cons: - Crappy headphones, weird battery cover, doesn't charge through USB connector, has 512MB card bundled, 1 GB wud've been welcome.
Am not a fanboy of Nokia or SE am just helping a fellow member. Any bashings will be taken seriously (am kiddin

)