Raccio - almost all lowpass filters in pedal form are also envelope following (the Moog and Xerograph included). Both of the pedals kevteop recommended can be used as a static lpf if you turn the sensitivity or range all the way down.
I've owned the Moog, and Behndy let me borrow his Xerograph for a couple weeks.
I'd say that the Xerograph is "cleaner", and the Moog is "synthier". i.e. the Moog has a more resonant, peaky, synthy quality to the filter sound than the Xerograph. It kinda depends what you're looking to do with it. If you want huge 70's synth sweeps, I'd go with the Moog. If you want to do like dubby reggae tones, I'd go Xerograph.
But that's just based purely on the sound. The Xero can get you 90% of the way to the Moog, and it takes up 1/4 the space and is true bypass, which the Moog certainly isn't (a lot of people really hate the bypass on the Moog).