A mac that doesn't get hot, doesn't make noise.

The faster it is, the more heat it is going to make, and in general, the noisier it is going to be.

Mac Pro is probably the quietest of them if for no other reason that you can put it under your desk or otherwise out of the way.

The iMac and Mac Mini are generally very very quiet. Though they may get a little louder when doing heavy work.

Any laptop generally "gets hot" when you are doing heavy work on it and it is sitting on your lap. And generally they are louder while doing so.

With what you plan on doing with it, I don't see any reason to get anything other than an iMac.

 

Don't go for the MBA.

 

Go with the imac.

 

I use Photoshop CS4 all the time and just made the move to Mac starting with a 27" iMac with a 3.06 C2D. One of the first things I noticed was the silence. I could not tell it is on by sound 98% of the time. If a disk is in then it sounds a little like hamsters on a wheel but other then that is is really quiet. Heat is not a problem at all and I do check this a lot.

I also just picked up a regular MacBook to go with my iMac. I got a great deal at MicroCenter.com for only $799 so I couldn't past it up. It too is nearly silent and heat is not an issue at all. Actually, I am amazed at how cool it is. If I pushing it then it gets slightly warm on the bottom and near the hinge but it is nothing uncomfortable at all and and barely worth mentioning. CS4 runs at a respectable speed on the MB. As a matter of fact I bought a 4GB set of Crucial RAM ($103) at the same time to punch up the MB to 4Gb but now I am thinking about using it to get 8gb on the iMac for when CS5 comes out instead. (CS5 will remove the current 3gb ram limit) so I can use my iMac for the heavy lifting.

Anyway, heat and noise are not issue in these macs running Bridge, CS4, and Photomatix

 

Perfect!

 

Have you tried to clean out the air vents at all on your 17" MBP? I believe one reason for a new computer running silent and cool is because the fans haven't had a chance to get clogged with dust yet...

 

try a cool mat?

If the laptop getting hot on your legs is your main heat concern the perhaps you would consider the following heat mats.

http://cgi.ebay.co.uk/Laptop-Coolin...Computing_LaptopAccess_RL?hash=item5d25640f55

I've had mine for 3 years and it cuts heat considerably so it doesn't become uncomfortable, my friend has one too and he also loves it.
Shop around for them though, picked mine up for £10 excl delivery.

 

I second the regular white Macbook suggestion. My friend just picked one up and I am shocked at how cool and quiet it runs - even while running Flash. The Nvidia 9400 seems to be really decent. I know they just updated the MBPs but I don't know how cool they are - and my experience has been they're always a little warm. Not so with the Macbook - I kinda want one over an MBP just for that reason. And for $800 it's such a capable computer, probably even more so with upgraded ram and an SSD.

 

Go for the 13" MPB it runs very cool and completely silent.

When gaming (which is actually pretty decent on the 320m!) the 'fan' kick in, keeping it very cool, still.

After quitting the game, it goes silent in less than a minute

 

My late '09 iMac is really quiet. I don't notice it at all.

 

Get the iMac

My 27" Quad-core iMac is the quietest computer I've ever used. Even during heavy work it is silent. I'm so happy with it and it's so fast!

 

Heavy work?

out of interest, what do you class as heavy work?

 

I have a 17" uMBP. I had a 15", too. Both are silent with an SSD unless you are running the CPU full blast long enough that the fans have to turn on. The fans are the only noise I ever hear, and not very often. An HDD will be noisy, but an SSD allows the MBP to be silent.