I just got a 20" C2D iMac last week and I have to say I am super impressed with it. I had a 12" Powerbook before, and although I think I might miss being able to take it with me sometimes, the iMac is better in every way. The screen is super bright. Front Row is actually very useful as I have the iMac hooked up in my bedroom to a 30" VGA Gateway Destination monitor. The thing is whisper quiet compared to my Powerbook and feels very solid. Also, compared to a G4 Mac it is insanely fast. I couldn't believe how fast it booted up the first time and ripping songs into iTunes is MUCH faster.
Also, I have been trying to stick to universal apps and I like iWork very much after useing it for a while. Just the time you save starting the program vs. Word will be enough to figure out its interface. Unless you are in need of the advance features of Word or need Excel, I would recommend iWork. It is fine, especially if you customize its toolbar. It saves to .Doc or .PDF so you can transfer files with everyone with very few problems.
My only complaint so far is that the backlighting on the display seems to be brighter in the lower right-hand corner than the rest of the machine, but it is barely noticeable and depends on the viewing angle. I am going to try to calibrate the LCD and see if it helps. I wish they would make an ergonomic mighty mouse shaped like many of those Logitech ones but I can live with it and it is nice having a right click.
If you live in an apartment or an area prone to burglaries, I would recommend getting "Lojack for Laptops" or some such anti-theft solution. (It works for desktops too). My girlfriends apartment was broken into and I wish I would have had that for her 17" Powerbook which was stolen. Unfortunately, if you are robbed, your beloved Mac will probably be the first thing they take.
As far as Ram goes, I would get it from New Egg. Use the tool on Crucial.com to see what kind you need and then buy from New Egg. There are several brands that will work and there are reviews from Mac users on there that can verify if it will work with your Mac. I think G-Skill, Gigaram, or Patriot have been popular of late but others may work too. Just make sure the Ram you get has a warranty.