Flowers, card, and dinner is nice.
I got my mom a digital picture frame last Christmas. She's been wanting one for a long time. She's also not very tech savvy (AT ALL), so I loaded a bunch of pics that I knew she'd like on there.
She opened it up and loved it, then asked how to get pics on there. I told her to turn it on and see if it had directions on the screen or something retarded. She turned it on and BAM, pics already on there. She said it was the best present anyone had ever gotten her.
In the end it kinda comes down to your mom and what she'd like.
Jewelry is also not a bad idea, and you can ask the people working wherever you go for advice (or bring a chick friend with). It helps if you have a vague idea of what she usually wears.