With many digital cameras you have to use proprietary batteries that are a lot more expensive than rechargeable AA batteries, but you do not have to buy them from the camera makers: for my Nikon D70 and the Canon Pro90 IS I go to http://www.powerinnumbers.com.au which is an Australian site with very good rates. They do delivery with DHL and you usually get the batteries within 3 days. No duty tax because the package looks too small to be interesting for the customs and they write "gift" on the package :)
A no name BP-511 for Canon 1450mAH costs there USD 15/EUR 11.6 while a "real" Canon BP-511A costs EUR 89 (almost 8 times more expensive!).
I have bought those batteries and they lasted much longer than the two original Canon batteries, with the exception of one that died quickly. The delivery cost is about EURO 10.
They also sell fast compact flash cards, portable hard disk for photos etc.

Olly

If i knew it before!! :o i have bought two batteries

Sophia

Ooops! :o
Don't feel too bad, I too bought batteries from Canon at high price before I knew. Let's save the money for the lenses :)
There is also a German site that sells batteries for a little lower than that Australian site but you need Paypal to pay them (or a bank money transfert). It is http://www.akkuinternational.de and there is no problem with them either. Quick delivery too.