Making a rain effect http://feeblemind.tuxfamily.org/dotclear/index.php/2004/12/24/4-blender-faire-pleuvoir---making-rain
Start by downloading this base file: makerain and open it within Blender.. Makerain-start.blend contains the starting scene, Makerain-final.blend the result of this tutorial. To get the very same result, you will need the optional plugin water available for download.
In Top view (Num 7), insert a new mesh of Grid type: (SPACE) + ADD + MESH + GRID with XRes:32 and YRes:32. Resize it up to the dimensions of the scene (S key) then in Front view (Num 1) grab it 10 units upward (G key).
In Top view (Num 7), now insert a Cone : (SPACE) + ADD + MESH + CONE with Vertices:8 then in the Editing (F9) menu activate SubSurf level set at 1 for both the preview and the rendering. Resize (S key) and move (G key) the water drop so that its center is at the center of the grid.
In the Shading (F5) menu give it a new shader and set its properties in the Shaders and Mirror Transp tabs. In order to shorten the rendering time of your animation, perhaps would you prefer to de-activate Ray Mirror and Ray Transp in the last Tab, and check activate ZTransp.
Select first the water drop and then the grid (order matters) and then parent them one to the other (CTRL-P, Make Parent)
Select the grid which will be your particles emitter. Go to the Editing (F9) menu, and with the object in Edit mode (TAB) click on the Flip normals and Hash buttons of the Mesh tools Tab in order to point the normal of your object toward the ground. In the Object (F7) menu, in the Anim settings Tab, click DupliVerts.
Then, in the Effects tab, click New effect, choose Particles and fine tune the properties of your particles system. For each of the objects in your scene that could be touched by the rain, toggle to Objet (F7) menu and in the Particle interaction tab activate the Deflection option with a choosen Damping level so that the water drops bounce on the object instead of getting through it.
In the Scene (F10) menu options, check Ray and MBlur in the Render tab, then activate and set the OSA value between 5 and 16 (according to your free time). In the Anim tab, press ANIM in order to render your animation.
