These are some of my favorite products to keep my hair bright and blonde! Most of them are drugstore products!
I use this product to refresh my blonde tone. It essentially looks like a glossy purple shampoo that you leave on between 5-15 minutes and you're left with brighter blonder hair after!
L'Oreal Paris Le Color Gloss One Step In-Shower Toning Gloss, Cool Blonde
This is another product I've used to refresh my tone. This is a toner and leaves you with an ashier look.
L'Oreal Paris Feria Power Toner, Long Lasting Anti Brass Toner