Which Mac to develop iPhone apps?
The current low level Mac Mini with an upgrade to 4GB memory is probably the best bang for your buck. That's what I have except with 8GB; got my memory from Amazon for $130, cheaper than Apple memory. It's a very capable machine. If you use a lot of programs simultaneously, the standard 2GB is kinda cramped, but 4GB would do fine; it just seemed like a good deal for 8GB and I use more than your average number of apps simultaneously and lots of Safari tabs.

The new MacMini is much nicer than the 2009's. I know this because I had one before this one; with 2GB of course :).

You're gonna love OS X by the way. Don't be surprised if you ditch Windows in a year.

About your specific questions:


Any current Mac has an Intel CPU. Apple switched from PowerPC back in 2006 and yes you need one, but you don't want a computer that old anyway!
Just about any keyboard or mouse will work fine with OS X. If you are using some kind of fancy mouse or keyboard, then you'll probably will need some third party software to get all those custom parts working, but all the standard parts will work; left click, right click, scroll wheel, cursor control etc. There is a chance however that there is no OS X equivalent of the third party software you may be using.
Finally, Macs work with standard monitors and even regular modern TV's with DVI, VGA, HDMI inputs (virtually all of them do). The most you'll ever need is a common adapter found at Best Buy, Apple Store etc.