Right now, B&H Photo has a list of major discounts that end on September 1st. You can get instant savings on a slew of different lenses. Take a look at the page.
But we wouldn’t be such great guys if we didn’t give you any guidance. Here are some of the lenses with savings that we’ve reviewed previous (with the accordingly linked reviews.)
Canon 8-15mm f4 L Fisheye Zoom
Canon 35mm f1.4 L (My bread and butter lens)
Canon 85mm f1.8 (another favorite of mine)
Canon 100mm f2.8 L IS and the 100mm f2.8 Macro non L IS (we’ve got a whole comparison here too)
Also remember that every purchase helps to support the site when you first click the according links and then directly make a purchase.