Historical returns for popular American funds over 20-30 years?
There are a few important things you need to consider when planning your retirement.

1. Risk tolerance.

You cannot invest only in stocks, whether indices or individual stocks. Even the most risk loving investors will get stressed out when their lifetime savings drop 10% over a week amidst some market volatility. It is usually best to put a portion of the money into bonds or other fixed income assets. They usually have much lower yields than stocks so it will bring down the yield of the entire portfolio. How much to put into bonds and how much into stocks depends on your risk preference and how old you are. The older you get the more you should allocate into fixed income assets.

2. Inflation. 

Inflation will eat up a lot of your savings over the course of your life. Not much can be done about it. Stocks are usually more resistant to inflation so having a decent position in stocks helps.

3. Hidden costs of index funds/ETFs

ETF and index providers sometimes try to hide some costs like annual fees, commissions for good performance, dividends etc. It is very important to look thoroughly into the costs of the fund you are going to invest in.

So if you build a balanced portfolio of stocks (index funds) and bonds, and the broker charges are either very low or free, then your annual returns on average should be around 3-5% depending on inflation. 4% is the rough estimate of returns you can get on a portfolio that is mostly composed of index funds. There are tons of literature out there, but most legitimate sources converge on the number 4%.

Here is an article from a good practical blog about retirement that I came across recently: http://www.mrmoneymustache.com/2012/05/29/how-much-do-i-need-for-retirement/. It has been featured on the Wall Street Journal so it seems quite credible.