Which Tall Plants?

@Mark359 I have fairly limited knowledge of available plants but Sue the moderator gave me some Hornwort Ceratophyllum Demersum late last year and I think it might work. It is certainly long and easy to grow, mine is putting on cm's per day. If you anchored some in the back left corner it wouldn't take long to have it up to the surface and the across the tank into the centre. Once it gets too long you just cut it back and start a second length or discard
It grew so well I am offering it (for free) in the swap/exchange section. If you would like some just PM me.

I'd thoroughly recommend Alternanthera rosaefolia; I have two of these in my tank and they've actually been thriving, one having grown particularly long, covering most of the surface of the tank (although I could cut it if I wished). They were advertised as medium-level difficulty to care for, which I was concerned about as I only started plant-keeping in the summer and even java moss (allegedly easy to care for) dies very quickly in my care, but these have been great and a good alternative/addition if you have green-coloured plants as these are a deep red. I haven't added anything to the tank for the plants and just leave them in their pots, but I rarely lose a leaf from these and have never needed to pluck any dying/decaying ones off.

My male platy & WCMM tank has H. polysperma, as does my tiger barb tank. They seem to like swimming through plants of that shape.
My tetra and hatchet tank has alternanthera, which adds a nice splash of colour considering the fish are all mainly silver. I got mine from Aqua Essentials because I wanted some big plants, but I have seen them at the LFS sometimes.
A lot of my other tanks have various amazon swords, which are very easy, and also various crypts, which seem to need no care at all.
I've also done well with most of the aponogeton bulbs.
I've tried all sorts of plants, and many have failed, but I'm not experienced and have hard water.

@fcmf Oooo that's good, a reason to visit. I work just down the road so I know where I will be Friday afternoon

Thank you all so much for the replies. I have had a look through all of your suggestions and I think I am going to order some Alternanthera rosaefolia and cabomba. I will post back a picture when they have hopefully grown up to the top!

@Andy the minion thanks for the kind offer of some Ceratophyllum demersum, I have done some research on it and I think I want to go for something that has roots rather than requiring some tethering