Ridgid is running a deal where if you buy 1 of their 3 Ridgid Jobmax Oscillating Multitools, you get a free attachment head of your choosing. Coupon must be presented @ Home Depot at time of purchase.
On a related note, I own (and am returning) the 18V multi-tool. Most of my tools are Ridgid 18V, but I find the 18V multi-tool underpowered. I tried cutting some old fir flooring with it using the factory packaged new blade, and it wouldn't make a dent. My contractor had the old 3.0 AMP corded version (new one is 4.0 AMP) and that thing cut through so much more effectively and with a dull blade. So depending on your need, the corded one may suit you better.
UPDATE DEC 4:
I went in to Home Depot to purchase, and you DO get the free attachment head on the spot. It's one of those "let me call my manager" to the register things but the manager seemed familiar with the promo. Note that many of the attachment heads are clearancing out and not showing up as active skus, so Ridgid may be running this promotion to clear the shelves of current attachment heads to make room for new ones. On a practical note, this means that you may have to drive around to get some of the lower quantity ones. I had to call another Home Depot to find the jigsaw head, but some of the others had much higher quantities.