Amazon U.S. currently has Lightroom 4 on sale for $40 off ($109.99). I do not know how long this will last.
Adobe has Lightroom 4 on sale for $30 off through May 11, 2013 in the Adobe store with coupon code SPRING 30. (At the moment the discount code is not working online, but from your shopping cart page you will see a number to call Adobe – they will give you the discount over the phone.) This discount code is also valid for Elements 11 and Premiere Elements 11, and is valid on all retail sales (not just commercial sales, as the website suggests.)
Keep in mind that Lightroom 5 is due out sometime fairly soon — the beta version is out now, and expires June 30. Speculation has its limitations, but this suggests that the official version of Lightroom 5 might be out before June 30 — unless Adobe decides to release a second beta version, which they did with Lightroom 3.