Haleyme..... As mentioned, SanDisk is the leading brand, not so much because of price, but more importantly, they are reliable.
You have a very large buffer in your 30D so read/write speed should never be a problem.
From the 'ultra ll' series on up you are in fine shape.
Even though I mentioned reliability, the 8Gb size card should only be considered if you NEED it due to shooting requirements. That is a lot of potential data loss. Accidents do happen, like losing or physically damaging the card.
My wife and I shoot together and we have found having 3-4 2Gb cards each comes in handy if we need to loan each other a card during sessions.
Swapping a card is less than 10 seconds work and easy to do. Buy a card safe that holds 2 or 4 cards and slide it into your pocket.
Having the largest card in the crowd doesn't count.