Boss BF-3

Great for the classic flanger sound. It's perfect for that heavily modulated 80's effect.
The gate feature also allows it to do a great job at emulating more extreme tremelo sounds, so it can save a lot of space on the board.
May be a little more complicated that its predecessor however.

I am very satisfied with my new BF-3, Great sound, easy to use, and the usual Boss quality. I use it with my bass. I recommend this product.

Boss make great pedals. This is the best Flanger. Strong build, lots of sounds no problems. Don't buy a shitty one, this is the one you want.

This flanger pedal is an excellent choice for both a guitar and a bass player. Guaranteed quality and clarity for your flanged sound, if you should need that. For me it is included in my standard setup.

This is the most versatile flange I’ve used in my life, it covers so much ground - I swear by it!

boss did boss things with this one. i don't need to comment on the build quality and sturdiness of this pedal. it can go from extreme jet flanging all the way to subtle almost chorusy type sound. it has some neat features like the momentary active setting.
all in all, if you're looking for a flanger that doesn't drop in volume when its on and just works doing flangy things, this is the one.