Unfortunately, some of the stations I think I would've admired are now closed down. e.g. Liverpool Exchange station (nice frontage at least) and Hadlow Road (on the Wirral).
As for stations still open, I like Marylebone station and Liverpool Lime Street too due to the improvements, it's much better than it used to be although they are still working on the main entrance. Manchester Piccadilly is also a great station, but I'm not mad on the through-platforms although I understand their position "out on a limb" is a matter of track layout.
For smaller stations, I visited Redland (Bristol) the other day and was very happy to see that it is was in better condition than it had been in previous years. I like that station, it's in a relatively nice tree-lined suburb too.
I like Birmingham Moor Street too, I want to visit again, I like the period feel of it and of course is very handy for New Street. Delamere on the Mid-Cheshire line is another one I like.
I also find that although most people seem to strongly dislike the dingy, moss-covered Green Lane in Birkenhead, I actually like it (hence my username).
Likewise, although I totally agree with the comments in the "worst stations" thread regarding the travesty of the rebuilt Euston, I've got to admit that it works well on a functional level, although I can't of course find it aesthetically pleasing.