Tamron is currently offering their “Tamron Summer Savings” sale on select lenses. Some of the deals they are offering are instant rebates while others are mail-in rebates. While I am not a fan of mail in rebates, Tamron has a very good track record for honoring theirs.
Since this is a Tamron special, it should be available from any Tamron USA authorized dealer. I have linked these special to Amazon.com searches for these lenses. Be sure you get a Tamron USA version as the international versions do not have any warranty from Tamron themselves nor do they honor these deals. Tamron USA products carry an industry leading 6-year warranty!
Generally, Tamron lenses are very well reviewed and can be excellent values compared to their comparable Canon, Nikon, Sony branded lenses. In fact, Tamron is also an OEM manufacturer of lenses for some of the Major camera manufacturers.