The law says IRA can not invest insurance, collectible, or self-dealing. Most anything else can be invested, including stock, fund, CD, small company, or rental/flip.
Only specialty custodian companies could do this, not the normal bank/brokerage, since they only want to sell their product.
There are some known companies that do this. Entrust is among those that have offices in selected locations.
One potential pitfall for self-directed IRA is self-dealing. Simply put, you can't buy a house and live in it (before 59.5 years-old), or rent it to your daughter. Also, you have to pay for all expenses from the IRA account.
Post here if you have any specific question, so we could discuss.
Helpful info such as IRS FAQ about IRA and news article about self-directed IRA maybe found here: http://www.sunskitehomes.com