Smart Product Filter & Search

Really nice filter menu that's snappy and customizable. And the customer service in terms of helping implement and adapt to your theme is top notch.

Update: taking one star off because I've had an issue where suddenly my collections broke and I had to disable the app entirely to keep my website functional. Looking around at alternative options, this app may still be the best option, but I will update if the issue is fixed or if I end up switching to a different app.

Update 2: adding a star back because they did fix the above issue reasonably fast, and the service for customization has been very good. It's not a perfect app, I'd give it 4.5 stars if I could, but despite the big hiccup, it's the best I've been able to find.