iMac or LED Cinema Display

It depends do you multi task (new screen) or do you need a new mac (new mac)
-Andy

It sounds like your MacBook is able to do everything you need right now, so I would definatly suggest the screen as your first purchase. Having 2 screens right off the bat should improve productivity with software and web dev (able to see what you're creating while you're coding for example). You'll also still have the option to take your work with you without much hassel which should help as well.

I say if you can afford it, get the imac.

I personally own the MBP 15 and was using it for my primary Mac as well. I just got the 27" imac and I am more than pleased with its power and screen real estate. Another cool thing is that you can use the Imac as an external display for your MBP ( or any other mini display port device for that matter). So if you do a good amount of work on the go, you can do so and then connect to your MBP to your imac for a 27" extension at home.

In terms of your question about the 2 monitors, once you start you will never go back. I love using 2 and it has increased my productivity so much. If you have any opportunity to A/B 2 windows, doing it on two monitors will be a lot easier. For example, when writing a paper, you can have one screen dedicated to your word processor and the other to a web browser for research. Another popular application for 2 monitors is using one portion of one screen for twitter and IM clients.

my $0.02. Hope it helps.

get the screen first. then get the iMac when you have the money. I find it so much easier to work on more than one screen. It even helps with everyday usage, just less switching windows

definitely the imac!!!!!!!!!!

I'd get an iMac if you're willing to spend the extra money because you can use it as an extra display too. But wait till the next gen model is released if your going to get it within the next 12 months.

First of all I'd suggest to wait to see if any new hardware revision of the iMac will be introduced. Although, if I'd have to make the suggestion, I'd buy the second screen first, as various people suggested above. (That is if the new Mac isn't compulsory.) More productivity would be better. You can always buy the new iMac later on if you'd so desire.