Once in a while I like to take black and white pictures because the EOS has a nice built in set of color filters. The easiest example of a nice black and white photo where a color filter produces great results is the classic “blue sky with Yellow filter”. You should really check out the great tutorials on Cambridge in Color.
When shooting in B/W mode, I often use the “sepia” filter, to add a little warmth to the photo. A wierd thing I noticed lately about the EOS 350D (besides the film transport sound) is that “Sepia” mode is not really producing pure B/W Sepia images. There is color seeping through! In the top image, you can clearly see residues of red, yellow and blue in a photo of a baby toy (cropped for privacy reasons). The bottom image is converted to pure B/W on a computer and then sort of “Sepia”-d using a hue/saturation tool just for reference.
I read on some forums that camera effects are generally not as good as the effects in image processing programs like PhotoShop or GIMP. This is supposedly because speed/quality tradeoffs. I really like to spend more time with the camera than post-processing, so I’d like to keep using the in-camera effects. A great tip I read somewhere on a forum is to shoot in RAW+JPG mode. The JPG will have all the processing done by the camera, and the RAW will be the raw data from the sensor. Depending on the results of the in-camera effects, you either keep the JPG, or use the RAW image to do the effect in GIMP later on.