Its a really good idea to think aobut fish first - that way you end up with the correct size tank and dont have to upgrade within three months. Take a look on the fish of the week threads and the resource centre
just had a quick read of the FOTW threads. It's quite daunting starting pretty much from scratch all over again!
OK, here's a few ideas....bash me on the head if they are not appropriate.
Flame Angel-
You can have but there usally around £60-£100
Percula clown - possibly a pair-
You can have a pair of these.
Goby & shrimp pair (dont mind which goby or shrimp, but must be a proven pair!)-
You can have very interesting and you don't need to buy a pair as they are very likely to pair by their selves.
Pyjama wrasse-
Okay but can be aggressive to other fish
Dartfish - firefish-
Very nice additions and are okay in your size tank.
Something a bit unusual - a frog fish perhaps?-
Not to familiar with these and are not that common so there maybe a reason for that.
Yellow tail blue damsel-
Okay in your tank but can be a bit of bullies especially with clown fish as they are from the same family.
Presume I can't have all of these in a 125L, so what would be a good mix?
Really need to go to a LFS to see more up close and personal.