Great post people!!!! I as an mechanical engineer would like to add a little engineering insite..... This comming off of what other people have listed.
First... Griffin... dude the activated carbon filter is awesome!!!! One problem.. its not thick enough to remove all of the smell. (unless you have a very small grow room... then it might work)
Second... Oregon Meds... AWESOME also. Only thing to consider is shipping....
What I would do as a grower and engineer is this.... go to lowes... they have 2gallon plastic buckets for like 2-3 bucks. Make sure you buy the lid too... its another dollar or so....
Take that bucket and on the lower sides of it (as in not the bottom but the lowest part of the sides towards the bottom of the bucket) Swiss cheese that sob all the way around the bucket. The larger the holes the better...(wouldnt go larger than 1.5 inches though) Buy the carbon filters that Griffin mentioned. (again Griffin... brilliant - props to you!!) Hot glue them to the inside of the bucket on the sides covering the holes. All the holes.... leave no hole uncovered. (even if this means that you need to drill less holes) Then, fill the bucket with the carbon that Oregon mentioned.
One thing that I would do however, is when getting those pellets that they sell... I would put them in a big ziplock bag and smash them with a hammer to get them almost pulverized. The smaller you get them... the more surface area = the better the scrubbing action = less smell.
Take the lid and cut a hole in it and attach your duct work to that. Once you put the lid on the bucket with the ductwork... it becomes air tight and all of the air gets sucked in through the holes in the bottom of the bucket. If you like, you can always screw the bucket to a wall or whatever before filling it with carbon if your setup needs it to be off of the floor.
I will be building one of these very soon. You can also use a mesh pencil cup and a mesh trash can (both from staples maybe walmart if you are lucky.) the the smaller one and wrap a nylon around it... then fill the larger trashcan with the carbon and put the smaller cup into it. Attach the ducting to the smaller cup. Only problem with this is the carbon if you get small carbon can fall out of the mesh holes on the trash can.
Hence the reason I will be using a bucket.
Hope this helps. Bucket etc is only a few dollars at any lowes. Carbon is your choice on where you get it from.... remember to watch shipping charges on it... and other than that.. you should be ok. If you lack a way to attach the ducting to the bucket lid.... check in the HVAC section at lowes. You might be able to get a ducting attachment to a box. It will have a flange on it that you can use. If you find it.. you will know what I am talking about. If you cant find that... get a 6in to 4 in reducer... only 7 something each (I just had to buy two) cut the hole in the lid at 4 inches and push the adapter through it from the inside out. The larger piece will keep it from slipping out. You can either use caulking to seal it up or actually... duct tape.
Once mine is built (end of the week or so..) I will post pics.
I really need to post pics of my growing rooms (hence plural) and my aero set ups. Perhaps next week I can do that. 800 plant capability in flowering alone and 400 plus mothers in the veg. All home built systems... and do not need to do everything at once. Its all add on systems as I grow.
All that college education is being put to good use
On an added note... I just found that a pet place called "that fish place" in PA has carbon filters for cheapier than what lowes does. They have a 3pack of carbon filters for 6.99 They are not as wide as what the lowes ones are however, if you drill the holes in the proper place that is ok. website is:
http://www.thatpetplace.com/pet/prod/206370/product.web
Feel free to look around for other carbon items there.
hope this helps...