SebastianK

This Plugin is very easy to handle. Just install with a few clicks and set it up in your configs. 
Then include it in your sidebar e.g. with the following code:
< ?php spWeatherShow(); ? > (without spaces)

spWeather

This Plugin gets the weather from google.de/google.com and shows the weather now and a 4 days forecast with tiny pics

Spectacula

interconnectit

Robert O'Rourke

AndyWalmsley

cm2creative

jackicit

Mim Mc

Weather information is pulled from the OpenWeatherMap API. This plugin adds a widget that can be dropped into any sidebar, can be customised to suit your theme and won’t hit any usage limits.
The widget can be configured as follows:
<ul>
<li>API key – required to get weather data from OWM, once entered it will be saved and auto filled in future widgets</li>
<li>Country – choose the country to get weather data from. (Some countries do not have an average result for weather conditions)</li>
<li>City – Enter the name of your area to recieve the weather results. If you want to use City ID, go to <a href="http://openweathermap.org/help/city_list.txt" rel="nofollow ugc">OpenWeatherMaps City List</a>.</li>
<li>Display Mode – you can choose to show either a compact view of the current weather or show the forecast for the current day and next three days.</li>
<li>Colour Style – Choose between two styles of colouring:
<ul>
<li>Style 1 – Primary colour: Background colour of current weather and font colour of forecast, Secondary colour: Font colour of current weather and background colour of forecast.</li>
<li>Style 2 – Primary colour: Font colour for both sections, Secondary colour: background colour of both sections.</li>
</ul>
</li>
<li>Primary colour during day – use the colour picker to choose what primary colour you want during the day time.</li>
<li>Primary colour during night – use the colour picker to choose what priamry colour you want during the night time.</li>
<li>Secondary colour during day – use the colour picker to choose what secondary colour you want during the day time.</li>
<li>Secondary colour during night – use the colour picker to choose what secondary colour you want during the night time.</li>
<li>Show Temperature in Celsius – sets the temperature display to degrees celsius rather than farenheit.</li>
<li>Show weather breakdown – choose whether to display the wind, humidity and written weather condition, as well as the temperature and weather icon.</li>
<li>Show Wind Speed in mph – sets the wind speed display to mph rather than km/h.</li>
<li>Cache Time – this is the interval in minutes before the plugin refreshes the forecast data.</li>
<li>Output CSS – toggle whether the widget should output it’s own CSS.</li>
<li>Show Credit Link – this plugin is offered completely free of charge. If you’re feeling kind please leave this in to send some delicious web traffic our way 🙂</li>
</ul>
You can override what gets displayed for the location by filling in the widget’s title text.
For info on how to use the shortcode, check the FAQs.
<h3>Known problems</h3>
Multiple shortcodes do not work if they are in the same post, as the data is stored based on the widget ID if displayed in a widget space or the post ID if using the shortcode. 
A new shortcode attribute has been added allowing you to add a unique ID to your shortcode which will be used to store data allowing multiple shortcodes per post.
This widget should work in all themes, although some themes styling will mix with the widget leaving bits that look out of place.
IE7 does not support the icons we use for the weather display. 
Works in IE8+, Chrome, Firefox, Opera, and Safari.

ICIT Weather Widget

The ICIT Weather Widget provides a simple way to show a weather forecast on your website.

spWeather vs ICIT Weather Widget