Ether's inflation is "linear," meaning it issues the same amount each year. This year, we started at around 75M and add 15M, for inflation of 20%. If we still had the same rules in 10 years, we'd have 225M, add 15M, giving inflation of 6%. The etherum's inflation rate will probably reduce once it transitions to proof-of-stake. Many people have the impression that it will stop entirely, but that's not set in stone at this point. The proof-of-stake algorithm is still in development so we don't know exactly what it will look like, and some of the existing proof-of-stake currencies do have inflation. Some ethereum developers have proposed zero inflation, others think a small amount of inflation will be better. What they have all promised is that the inflation will be no higher than now.
Note that with fiat currencies, inflation generally refers to price inflation, not absolute currency amounts. As long as you don't grow your currency faster than you grow your economy, prices are stable.