In searching for a deal on the TI-89 for my sister going back to school, I couldn't find much. Just for kicks, I tried a $30 off $150 OD online coupon and to my great surprise it actually worked. Apparently, the TI-89 is NOT considered a technology item by OD, which is why I'm posting this as many people probably are not aware of this fact and the AC price is lower than at any other major store.

1. Go to http://www.OfficeDepot.com/promo.do?file=/promo/pages/coupon_30off.jsp and click "SAVE NOW". Alternatively, you can just add coupon 076902528 to OD cart. Coupon expires 12/31/08. This coupon can be used by anyone but can only be used one time per Office Depot account.

2. Add Item #503376 Texas Instruments® TI-89 Titanium Graphing Calculator to Cart for $149.99.

3. Add filler. My filler was item #571081 Office Depot® Brand Glue Stick, 0.7 Oz., Clear for $0.79 because I did in-store pickup and couldn't find a lower priced filler that was available for in-store pickup at my store.

Curiously, this glue stick is now showing up for $0.99 in OD system. For delivery order, item #808873 ACCO® Premium Silverette Paper Clips, No. 1 Regular, Box Of 100 for $0.49 would be cheaper. I'm sure you guys can find an even cheaper one, however a lot of the cheaper ones I found say "this product is not available online."

Final ~$121 + tax in your area ($7.15 for me in Georgia). Next business day delivery is free for OD.com orders over $50. Obviously no shipping charges for in-store pickup either.

Comparison:
Amazon.com $135.84 with free shipping and no sales tax for most

Staples Item #566640 $154.99 - $25 off Staples Coupon + ~$2 coupon cost = ~$132 AC + tax

Circuit City $136.99 + tax w/ FS

NewEgg $135.99 + $8.97 shipping = ~$145

Best Buy $154.99 + $4.99 shipping = ~$160

For the record, xnlc on SD already posted something similar to this, though it wasn't the TI-89 Platinum. Instead it was for TI-83s, TI-84s (silver and plus editions), and TI-Nspires. There were two $25 MIRs you could use with them and a $20 coupon for all of them (with the exception of the TI-Nspire which had a $30, being it was over $150).

http://forms.young-america.com/83652_OD6602027-06242008.pdf (first MIR)
http://forms.young-america.com/84124_OD6602028%2007-17-08.pdf (Second MIR)
Coupon code "42206472" (expires 9/13/08) $20 off

After all that, some of those calculators come down by $70 in price.

(I'm sure this post will be edited some, as I haven't fully read the rules yet, though I hope this helps. Not even sure if this is a repost.)