The Canon BG-E1 Battery grip or vertical grip as it's sometimes called is an accessory often overlooked by many amateur photographers. Besides the obvious of adding capacity to shoot off two batteries instead of one, there are many intangible ergonomic functions to the grip which are of even more importance.

The front of the Canon BG-E1 Battery grip. On the bottom is the quick release plate for my Manfrotto Tripod which is not included.

Having always had a battery grip for my Canon Film EOS camera adjusting to the 300D or Digital Rebel without a grip took some adjusting to. In the end I broke down and opted to buy a used grip on eBay. The grip allows you to hold one extra battery to extend shooting time. This makes extended shooting very convenient especially when it gets cold up here in the winter. If you find the camera heavy however you can still shoot with the grip with only one of the battery slots occupied. This isn't like some other Canon grips that use both batteries simultaneously. My understanding is when the first battery is drained, than the grip switches to the second battery.

The grip is meant to be used vertically. So in this image you would rotate it 90 degrees counter-clockwise. Than all your essential camera controls are at the top again.

One other excellent thing the extra battery grips allow you to do is since you actually are shooting with the camera vertical, and that's the way the controls are set, there is no reason to turn the camera back to horizontal after taking a photo.  That means you can turn off auto-rotate in the 3rd menu of the 300D.  This applies to all cameras though.  Think about it, since your holding the camera normally vertically, you can view the photo in the same manner.  The camera has less processing work to do on the image preview, and you can view the photo full size in the screen.  This is a huge thing for us 300D users because we are stuck with a relatively small LCD screen and the 300D is a relatively slow camera as well. 

Here's a tip.  A know many people who have never read through the instructions of the things they buy.  For all Canon battery grips I have ever known including the BG-E1 there is a place to store the battery cover you had to remove to insert the grip.  On the BG-E1 it is located on the part that inserts into the battery compartment. You simply slide your cover in.  For those of you with the BG-E2 or BG-E3 it's actually more of a little hole you slide the cover into.  Make sure you use it otherwise you'll lose your original cover.  Trust me. 

I love the extra weight and feel of the grip. For those of you used to larger or pro bodies the BG-E1 and other Canon grips are essential. I find this even more so on the Canon 350D or Rebel XT. Without the BG-E2 grip for that camera it is extremely unbalanced and lens weight biased. In other words with a decent lens on the 350D and no grip the camera tips forward in weight and is very awkward to use.