I'm fairly familiar with names, their histories and trends in general, so it's rare that I come across one I'm unfamiliar with (except for certain names traditional to other cultures/languages, of course, but I can't remember most of those offhand). I HAVE, however, been quite surprised to see a few of my more-obscure favorites mentioned here, on occasion. ;) Always intriguing to see some of these considered or suggested by others!
Isla - to use one of your examples
Matilda
Niamh
Imogen
Freya
Harriet
Eloise
Harvey
Finley/Findlay
Ewan
*** all of the above rather common (mostly top 100) choices in the UK, but many not yet in the top 1000 in the states. ;)
Devanie
Fiora
Talulla (or more commonly, the separate Tallulah form)
Gwyneth
Romilly
Adelia
Annora(h)
Clodagh
Isadora/Isidora
Finola
Aveline
Avalon
Calliope
Xanthe
Ronan
Cillian
Finnian
Dexter
Fletcher
Lachlan
Lennox
Milo
Jasper
It's always fun to see others considering attractive, underused options. ;)
Edit: Wow! Snow Globe is a top contributor and doesn't know that these are actual names?
Willow - a fairly obvious nature reference (and if that's not "real," neither are Rose, Lily, Dahlia, etc. LOL)
Gianna - a common short form of Giovanna, stemming from masculine Giovanni, the Italian form of Johannes/John!
Eliana - an old, even traditional, Hebrew name (meaning "God has answered," for what it's worth)
Piper - a classic occupational surname referring to a flutist
Cadence - a recently revived word name simply referring to rhythm or flow, but just as "real" a name as Felicity, Rose or Faith.
Talia - another Hebrew choice meaning "dew from God"
Seriously, can we take away those points? LOL