Snow, balloons and more (nksnow) free WordPress plugin

Snowflakes (and more) falling down your blog! There are snowflakes, leaves,
drops – and balloons that can float upwards. You can simply add more images
in the pics folder and they will appear on the settings page. I also happily
accept images submitted to me as long as they are properly licensed.

You can configure the number of snowflakes and limit the plugin to specific
posts or pages. If you enter something into the URI field you will only see
snow if the URI of your page matches the string. No fancy regexps.