"Are there any limits on the amount that I can claim as a deduction?"
Yes, the limit is generally 50% of your adjusted gross income. This means if you have income of $100,000 and you donate $60,000 to your church, your deduction is limited to $50,000. The remaining $10,000 is carried over, and is available as a deduction for up to five additional years.
Gifts of certain things such as appreciated property have limits generally of 30% of your adjusted gross income. This would include things like the gift of low basis stock to Harvard.
There are other limits based on what type of organization you are donating to, but we rarely see that.