Why would I want to open an IRA?

[TheMetetron]

Okay, I'm doing my taxes for '05 and I am trying to understand the logic behind an IRA. Why would I want to put 40k (I think the maximum is) into an IRA?

Sure, I don't have to pay taxes on it now, but I will when I withdraw it, correct? So what's the point? I either invest it on my own, pay taxes on the principal now, and pay taxes on the interest as I go along or I pay all the tax later (but I can't touch the money for almost 40 years).

I can't see why anyone would want to do this unless their company was matching contributions. As a self-employed person, I don't see the point.

Try to convince me otherwise?