You can use Gmail without ads if you pay USD 50/year/user for Google Apps for Business:
I don't disagree with those of you who were a bit surprised to find this application blocks all ads indiscriminately. I also find Google's ads to be the least intrusive on the block. One need only login to Yahoo! Mail to realize how unobtrusive Google's ads are.
A major issue would be the migration of your data from your private Google account to a Google Apps account. There is no direct migration path, you basically have to download all your data and upload it again. If you have a high number of mails, it might take weeks since download/upload are rate-limited.