Thanks for the in-depth reply, Rounik.
I'm a semi-professional using the computer mostly for orignal music and band applications. I have to admit I'm using a downgraded version of Cubase right now, but have heard a lot of good things about Logic and want to look into upgrading.
I use a lot of keyboard sounds (via computer and external modules) but do use live bass, guitar and vocals. I have a couple of plug-ins at the moment but will acquire more as time goes on when I feel I need them.
The other uses would be photoshop, video applications, etc. Nothing too extensive, but keeping my options open.
I'm thinking the iMac might do what I'm looking for. Regarding the Mac Pro, although looking much more powerful, I don't think I can justify spending the money on that right now.
Would you recommend the 21.5" screen, or the 27"? Should I spend the extra $$? If I bought the 21.5", I would use a second monitor as I do now. Is it personal preference, or is the 27" a better computer?