A little update on the list (no guarantee!) as I could see it just now:

Rodzaju - -4 (evil! :p)
Zchinque - 8
TheCheese33 - 10
lackoo1111 - 12
lalowei - 13
Stelis - 13.5
MoP - 14
Ralackk - 14.5
Austrobogulator - 15
saramakos - 16
olgar - 17
reaver894 - 17.1
Lockmat - 17.5
phenom_x8 - 18
acemarch - 18.5 (if he may choose a different number because the first was taken)
kazmar - 19
Catshade - 19.5
Darling_Jimmy - 20
park_84 - 20.2
Gilou - 20.25
Fujek - 20.5
Palehorse - 20.8
SLP2000 - 21
Smannesman - 21.5
Tallima - 21.75
taczillabr - 21.9
Aningan - 22
csmith - 22.2
barbu67 - 22.4
tarangwydion - 22.5
Roman5 - 23
nmillar - 24
KavazovAngel - 25
liquidsnakehpks - 26
RealMikeBob - 27
Balthier - 28
Immoli - 100 (*grins*, if he wins I'll gift him an extra GoG of his choice :p)

And, amusingly enough, an amazing 22 people that either edited their posting or took a guess that was already held by another person (with one edit being an accident and one missing the already taken number ;))
For the sake of in dubio pro reo, I'll guess those that took an 'unavailable' number are hoping for an 'edit' of the ones that had the number first *grins and winks*

I'll take a shot at 27 since most of the likely ones seem to be gone. Although 27 would be great I imagine!

22.2. Partly cloudy with a chance of beer!

21 and cloudy

my bad, missed the guy who put 19, so revise to 18.5

I'll throw my vote for 18C, partly cloudy.
I missed the bit about only one person being able to hold a number, so i'll revise to 18.5 if at all possible, if not, no biggie since it was my fault for not paying more attention :P

Good Luck to the everyone else ^.^

All the good numbers are taken... anyway, 22.5 degrees and sunny...

22,4 sunny. Have a great party!

It'll be hot as a Terror Site, with a slight chance of nuclear winter and occasional headshots.

Okay, easy. It will be hailing and it will be.......100 degrees celsius.

20.2C

I guess you missed the 'not edit your post' part as well :p

Cloudy, with a chance of meatballs.

I'll do mainly sunny, high of 20.8

14.5 and cloudy.