First time purchasing iMac - Your thoughts?

I am a basic Mac user (maybe minor web design - mostly for hobby & blogs etc.) and have Photoshop CS4, again just for hobby...this is not my career nor am I trying to make it one. I just happen to be a PC convert and have LOVED every minute I have used a Mac (2 iBooks, MacBook, and MacBook Pro). I donate (and convert) my family/friends w/my older macs when I upgrade and I'm getting ready to purchase my first iMac.

My options: (I'm faculty at an educational institution, hence the discount)
$1262 - 20" model w/upgrades to 2GB memory and 320 GB HD 128MB Graphics
$1399 - 20" model w/standard 2GB memory and 320 GB HD 256MB Graphics
(is the difference in Graphics worth the $137?)

Or

Should I wait. I'm in no real hurry to get the iMac, but as I'm sure any Mac user can attest I'm really eager to get on a new machine. Can someone explain what the benefits of waiting might be. If I could get a 24" for roughly the same price and all I have to do is wait until January (I've heard rumors Apple will be announcing some big changes to the iMacs), I'd MUCH rather wait. If it's a little faster processor I think I'd just get one now. Thoughts?

Or is it safe to pull the trigger, if so, which of the above would you recommend? Which is the most "bank for the buck"?

Thanks in advance for your input!!

Well, I didn't need a MAC but got one just because I love the fluid look (mainly the dock) of the OS (MAC crashes often too!). The beautiful design was icing on the cake too. Apple was also smart enough to let you run Windows, which I really need for work.

Get one, you won't regret it. I'm not really a switcher, but would like to know knowledge of both worlds.