This
pruning loop from Plant Guild products seems like a good product. You can order different lengths as well if you really want. I saw one person who had it was selling it. He said it worked well on stem plants, but not so well on thicker type plants (like anubias and such). Just what I remember. Definitely don't quote me on that.
You can also buy long handled scissors. Also, the various aquarium supply stores on-line carry these gigantic tools to trim plants, but they seem more appropriate for ponds or a big aquarium.