Stand-alone Navigation?

My wife recently got a 2005 GMC Sierra Crew Cab.  It has the Bose head unit with OnStar and XM.  She wants to keep both OnStar AND XM, and she has no problem with the sound quality of the factory system.  I want to install a stand alone navigation system, but I do not know what kind of systems are out there.  Most I see in the local shops are Recievers as well, which I don't need.  I would like to integrate this well into the interior, and there is an empty DIN sized hole in the vehicle already (the Denali has the CD changer there).  So, my questions are as such:

1.  Are there any decent standalone navigation systems that will fit in that DIN slot?

2.  Is there an acceptable way of connecting the voice prompts of the navi to the factory stereo?

Thank,

CraziFuzzy

Pioneer has a stand alone 6.5 inch touchscreen w/voice guidance & voice input (NAV-SYS620T). http://www.pioneerelectronics.com/pna/product/detail/0,,2076_3151_117424985,00.html

Nav brain is an AVIC-88DVD, DIN-sized unit - the screen is a AVD-W6210 6.5" widescreen touchscreen. You would have to find a place to mount the screen for the driver to see & use. The AVIC will probably fit in that hole, but the unit has to be mounted fairly level to work the best(or under a front or back seat).

For the audio - there is a jack on the back of the AVIC-88DVD to use an external speaker. SOUNDGATE makes a device (GMCELL) to interrupt the factory radio & bring in the audio from the phone. I don't know if this will work if you have OnStar - you'll have to call Soundgate tech & ask. Their website hasn't been updated in a while - the GMCELL has a retail price around $40.