My main pen collection consists of Kikki K pens - my collecting began towards the end of last year when I started visiting their stores again quite regularly. Like most designs, the Kikki K range changes from season to season, so only the latest ones are available to purchase in their store. To buy the previous designs, you'll have to try and find it from other sources like Ebay. I managed to find rare pens from years ago, which included their Under the Sea mermaid pen - gold!!
Other pens I've been collecting are the Target USA dollarspot pens, as well as the mechanical pencils. I've bought a few from Etsy and some were given to me by my cousin in the states, but most have been through stationery swaps.
So far, here are my pen collections in various photos.
Update October 2015: I have received more Target USA pens and pencils from a recent swap and have also purchased more pens from Kikki K and other stores. More photos added! :)