see the thread "mini mac value?" by truewrestler for some other info. Right now the best value macs are (in my opinion) the eMacs and the iMacs (especially the iMac 17"). Rumors are saying that the iBooks are about to get a long over due update. They normally update them ever 5-6 months or so, it's been about 9 months now. There's also been talk about a mac mini update. I personally feel that on the notebooks if you look at the 12" iBook and the 12" PowerBook, that the cost/performance ratio favors the iBook, I just don't feel there is that a $500 difference (50% the cost of the basic iBook). However (before other mac lovers come on here and flame me), that's straight up PERFORMANCE differences (yes I realize the 12" powerbook has a faster hard drive, faster RAM, and faster FSB, but that still doesn't create enough of difference for me), but the PowerBook does come with other features that you might value more, such as the sudden motion sensor on thte hard drive, 64MB graphics card, 3 speakers, and other differences. Also, the rumors for the iBook update have been all over the board, everything from a simple speed bump, to a complete redesign has been rumored during this longer thten normal wait on an update.
As for the free iPod it's the student discount deal going on right now. If you buy just about any mac with a student discount (mac mini and base model iBook are excluded) you get your regular student discount and a $180 rebate on the purchase of any iPod and iPod mini. Since the base model iPod mini is $180 you can get that for free (still have to pay taxes) or you can put the rebate towards any other iPod or iPod mini.
"I already have a laptop, should I consider getting a Mac laptop? What is the battery life on the different Macs compared to Centrino P-M Intel Dothans?"
It depends on what your needs are and what you want to do with the mac. On average Mac notebooks have better then average battery life, don't get me wrong I've seen some P4-Ms that crush the Apple notebooks on battery life, but like I said on average the macs have better then average battery life. They also run smother and much quieter...although the P4-Ms are catching up in that department.
"if I get a Mac laptop, which ones are the best for wireless security auditing, i.e. have monitor mode on their wireless and lots of expandability (dual PC Card slots, Firewire, USB 2, etc.)?"
I would say they're all about even with one another in regards to wireless security auditing. The only thing I would mention is that from what I've seen and heard iBooks tend to get better wireless reception then the PowerBooks (they also tend to get better battery life then the PowerBooks, but the PBs do have more power). Also, it's worth mentioning that currently with AirPort Express Macs can not passively monitor a network. The older Airport cards can, but not the AP Express cards. Also, because of OS X's BSD base there are a lot of nice *nix apps that have been ported over, do a search for Fink for more info.
As for the expandability only the 15" and 17" PowerBooks have dual PC Cards. None of the other Mac notebooks have PC card slots. All Mac notebooks have Firewire 400, again only the 15" and 17" PBs have Firewire 800. All their notebooks have USB2. Also, on a Mac the firewire drive can be a bootable drive, USB is not supported as a bootable drive.
As for what you should get it's really up to you and what you plan on using the system for. Also, you said you have a notebook, but do you currently have a desk top system? Unless you have plenty of space on your desk then an eMac or even an iMac will mean a lot of your desk space is taken up by two monitors (sadly you can not use an eMac or iMac as a display alone unless you use some kind of remote desktop system to access your other system, but no KVM or video-in feature).
Personally I'd say figure out what you want to get, or narrow it down to a couple of models. Then start checking out the going rates on them, check ebay, craigslist.org, and apple's site (both the store and the refurb section...but when checking the store don't forget to factor in your student discount). Once you know what you want and what the going prices are on them (both used and new) then start shopping and jump on a good deal you see.
And let us know more about what you plan on using the system for if you want more help with figuring out what'll work best for your needs