A lot of times I will be working on a project and they want to come out and be with me, so 50-100 ft range is perfect for this application.
For 50-100 feet outdoors, the XBee should work well. I use the XBee Pro inside (through multiple walls) and it works pretty reliably at 60 feet. Given your application is not super time sensitive (dont need to detect in milliseconds), that helps with reliability (you can resend multiple times).
I can think of several ways to use the RF link available from Sparkfun but I like the X-bee because of the serial capabilities.
The XBee is a nice all-in-one package. It has worked well for my applications, though I wish it had a bit more range. I use a combination of XBee and XBee Pro modules. Interfacing via a microcontroller is pretty straightforward. Biggest problem I ran into on my current project was running out of code space. I used a AVR2313 which only has 2K of Flash and maxed it out.