Tyder Ltd
Provides digital filter design software which can produce specialised filters e.g. Windowed FFT, Optimal FIR filters, and IIR filters.
http://www.tyder.com/

Simple Filters
Easy to use filters for enhancing Photoshop and Paintshop Pro - Not available anywhere else!!!
http://www.btinternet.com/~cateran/simple/

Simple Filters
Easy to use filters for enhancing Photoshop and Paintshop Pro - Not available anywhere else!!!
http://www.btinternet.com/~cateran/simple/

OPT Hellas Custom Frequency Control Components
Manufacturers crystals, crystal filters, lc filters rf and microwave filters. Descriptions and catalogs and international sales network.
http://www.opthellas.com

Soot-Vac
Soot-Vac - Industrial tube cleaning systems
http://www.soot-vac.com

Reclaim filters and system, Inc.
Reclaim Filters brings you reliable and economical solution to your basic filtration needs. Clean and recover your water with our filters and filter systems. Based in Wake Forest North Carolina
http://www.waterreclaim.com/

Sponge Company, Inc.
Dry Cleaning Sponge, Soot Sponge, Chemical Sponge, Chem Sponge, Soot Sponge.
http://www.spongeco.com/

Kemo Signal Filters
Electronic filters, a full range of systems and modules
http://www.kemo.com/

Lee Filters
High quality camera filters, lighting filters, gobos, and other studio-related products. Camera Bellows.
http://www.leefilters.com/

Firmament
A set of plugins with terrain import filters, terrain manipulation filters and images filters. Download only for windows.
http://www.mclusky.co.uk/firmament/