Here is weatherbug direct, it will put and icon on your home screen with the temperature shown in the icon. When clicked the icon will take you to the weatherbug mobile website for the rest of the information. Its not that great of a weather program, but if you are looking for something free with a thermometer.....It'll work.
Just go to blackberry.weatherbug.com from you blackberry browser to download.
Beweather(berryweather) has the thermometer icon in the banner. It does not work for 4.5 os, not sure about 4.6/4.7. My friend has a tour with 5.0 and it works on that just fine.. This is for the icon in the banner at top of your screen, not for the icon that sits with your other app icons. Beweather is the only one I've seen with that feature. Hope this helps.
Posted from my CrackBerry at wapforums.crackberry.com
BB Weather is completely free and has an icon that can be placed on your home screen and it will automatically update with a picture of the condition (i.e. sunny, rainy, cloudy) with the temp displayed. Many of the custom themes available have a slot for your weather icon in the top banner. Like mine here for the 8350i.