Let's pull out the stops...

WxWorx Mobile ThreatNet on a laptop, and any GPSr that will also hook up to said laptop & provide NMEA compliant data out a serial port from the GPSr to go into the laptop. The software & receiver for weather data (XM Weather) will cost you about $1k. You then have to come up with the GPSr and laptop to make it all work.

The only Garmin units that currently have NEXRAD are marine and/or aviation units. Like the GPSMAP 376C or 396. The caveat is that they, of course, wouldn't have traffic info.

Otherwise, I'd say the Garmin 7200 or 7500. They are designed for use in a truck or an RV, but they aren't waterproof.

I am running a 376c on my Harley with no problems from vibration or weather. To get the weather on the 376 you have to subscribe to a XM weather package, be sure to use a marine package NOT an aviation package. When you get a weather package you can add XM radio for 6.99 more and will give you the traffic up dates for most major cities. Go to the XM web site for more details.When you add the City Navigator 2008 mapping software and the 512 mb memory card to this unit, you will be looking at between 1,300 and 1,400 $. I DO NOT advise buying any of this any where other than a AUTHORIZED Garmin dealer. Check the FAQ's on the Garmin website.

I have the Nuvi 360 and 376 mp's on the 2 gig sd card and I have XM satellite radio for weather and anything else I might want to listen to all for less that $12.00 a month. I love my toys....LOL