I would stick with SD (Secure Digital) Memory stick is a proprietary sony format SD is much more portable to other brands. I would go for the 1GB and I would recomment the A-Data brand high speed stick. Available at :

Here is a link that might be useful: AData 1GB SD Card

I agree with choosing SD over the other choices. However, I would counter the recommendation of going for one big memory card. Many people I know with digital cameras tend to leave the pictures on the card for a long time. If anything happens to that card (it gets lost, it gets corrupted and files are damaged, etc.), you stand to lose a lot more than if you had all those pictures on two 512 MB cards. And if that's the card you tote around with you and something happens to it, you may end up buying another card just to have some "film" to use. Just something to consider before you put a lot of your memories on one piece of silicon.