You can purchase IOUs (be sure to use escrow) from the IOTA Speculation thread.  (Often linked here, to lazy to find it.)

If you prefer to wait until it hits an exchange, I think this is still one worth purchasing when it is listed.  I don't know why but from general scuttle here on BTT, Waves and Lisk are the ICOs getting the most attention but I think iota has the most potential for greater real world adoption and success.

David (iotatoken) and many others in the community are working crazy-hard at getting the word about iota out to actual companies and organizations that are forming the emerging IoT ecosystem... and they are succeeding.

If you do decide to invest, please get plugged into chat (chat.itoatoken.com) or the official forum (forum.iotatoken.com) and help where you can.  At a minimum, you can download the next client update (which will be 0.9.1) and request some iotas from fellow users.  We can send you some and you can help test the network.