I have had some bad luck with the Apple remote and Keynote. It works for a while then stops working. I thought it was the batteries. Later figured out it just gets jammed somehow. Maybe it is just Keynote or just my laptop. Other than that the remote works well. You don't have to aim directly at the Mac. The IR is really bright so you can usually aim at a blank wall or screen where the Mac is facing and it will respond. They might let you try one out at an Apple store.
The presenter remotes I've seen were pretty simple but they worked well. They usually just emulate a mouse click to go to the next slide. Try googling usb remotes and see what you get. Find one with right and left arrow keys so that you can duplicate what you have on the keyboard.
You can try setting up an ad-hoc WiFi network and connect by that to the iPhone remote app. Again, make sure it works in the presentation room, not just at home.
One thing that used to work really, really well for me is Salling Clicker. For this you need a fairly simple cell phone (not an iPhone) and their software. You could probably pick up a compatible Sony Ericsson or similar for nearly free. You don't need the cell phone to work, just the bluetooth. Salling Clicker provides an amazing amount of control of your Mac software.
