I am getting my mum an e-reader for Christmas and I wanted to load it up with a few books to get her started.

Does anyone know any trusted/safe sites to purchase the books from?
I have googled but have no idea what I am looking for really or how to tell what sites are legitimate.

Also can I start getting a few now before I have purchased the e-reader or do they have to be in a certain format for the specific device?

Depends on the e-reader. Some can use multiple formats, others you have to buy from the device store.

I have a Nook Color, my wife has a Kobo. She buys from the Chapters online store, I use Calibre to load all types on book formats to my Nook.

Lots of free ebooks can be had: 391 Places for Free Books Online

Thanks Scott and NK, I'll have a better look into what brand I want to get before I download any paid ones.

Thanks for the link, very helpful will be bookmrking that one.

For public domain books check out http://www.gutenberg.org/ the offer classics in several formats.

Thank you cmeeks I'll check that one out too.