I now have a few whistles in D and a fair number of tunes under my belt. I’d like to experiment with whistles of different keys and wonder if anyone has a recommendation of “the next key” to try? I play solo and tend to like whisles that have volume that carries. Any suggestions?
C and Bb (sorry, these are two!)
I always preferred Bb for playing on my own. Also much more family friendly than D.
C is great as it can be useful for playing stuff in that scale, and not just transposing (playing your D tunes on the C or Bb whistle).
As to volume: this depends much on the whistle design.
~Hans
Get hold of a Generation Bb. They are great, and most of the Bb Generation whistles I have tried, have been quite accurately i tune.
I usually stick to low whistles, but when I am gonna use a high whistle, I tend to go back to the Bb whistle.
If you were playing with other people, I would say C. Since you’re not, Bb, you’ll like the big difference. If you’d like a really big difference, get a low D, you’re going to anyway.
You will get a lot of Gen Bb. That is my vote.
If you have a D whistle and can play in two sharps (E concert) and one flat (G concert) then you are actually able to play in three major keys and their three relative minor keys on the one whistle. Adding a C whistle gives you another 6 keys to play in. Then adding a whistle in a flat key (Bb or Eb) is the next thing worth doing.
Over the years I have mainly used D, C and Bb, but I did have a rather nice 1970’s Generation Eb that was very useful.
So I would say go for a C next and then a Bb (or an Eb if the fancy takes you and you can find a good one thats not too expensive).
For what it’s worth, the best whistle I have is a Jerry Freeman Mellow Dog in C.
Most every one has a Generation Bb, and enjoys it. 
I have one, and also a Generation Bb tone tube cut down to play in the key of B. Thing is though they are very mellow, and then you will be wanting a low D. And then… etc …?
If you don’t know what key you need, you don’t need a new key. Right? 
Anyway, Gen Bb is the best Bb whistle I ever heard. Get one, they’re cheap.
I’m going to go with the crowd and say Generation Bb. I just got one a few weeks ago and I love it to death. I do, however, also love my Dixon Trad Eb very, very much. It’s so easy to play and sounds absolutely beautiful though it’s not very loud. Both are pretty affordable…the Gen Bb is downright CHEAP (I paid about $8) and the Dixon Eb is about $30 at Whistle and Drum. (I think I paid $27, but don’t quote me on it.)
Is really Bb more useful than a C? 
Because, in our band, we get by with a D and a C. But, we are almost total amateurs. We were thinking of getting a G, but now i hear all this fuss about a Bb, so i’m interested.
And, oh, please, could someone tell me which whistles the Dubliners are playing in this song?
http://www.youtube.com/watch?v=Rhpb_-QGPQ0
I mean key-wise.
Is really Bb more useful than a C?
What you want, what you need and what is useful to you are three different things.
Gen Bb is a great whistle, but the fiddler will kill you if you ask him to transpose Cooley’s to Cm 
Also, if your band not only plays tunes, but also sings, then you have vocal range of your vocalist, so it’s not you, but him who will choose the key of your whistle. And so on.
Finikey is playing by him/herself so I would think that the actual key of a whistle doesn’t matter so much as a different sound. The material of the whistle makes a big difference too. Finikey, you may want to consider whistles made from different materials, like wood and bamboo to get a whole new sound from a whistle.
Let us know what you decide. We’re nosey as all get out.
We’re nosey as all get out.
Speak for yourself, man. 
Those would be Generation Ds, played in D (and tuned a bit sharp), the high one going up to a 3rd octave e’.
As Mutepoint says, if you’re playing with people, get a C, and if you’re playing on your lonesome, get a Bb.
It may colour your decision if you think you might get to play with people.
…and after that, get a (low) high A…
Thanks, MT. 
How the hell he managed to get a 3rd E on a Generation like that? 
By blowing faster. It’s not that hard
once you get the breath control down.
I’m more impressed that they were able
to play 2 whistles together in tune.
Yep, Generations easily play that e’ note with xxoxxo fingering, no need to blow hard at all.
Having just been rediscovering my gen Bb and Eb whistles I would say try one of those - much nicer than a gen D. The head of the Eb was partly broken and so I swapped the head from my D (both were blue with silver colored bodies) - the Eb is special, the D nothing special, so its not the head that makes the difference in this case. Of course playing in a session with others in those keys … might be good if you want a solo.
A little typo probably:
If you have a D whistle and can play in two sharps (E concert) and > one flat (G concert) > then you are actually able to play in three major keys and their three relative minor keys on the one whistle. Adding a C whistle gives you another 6 keys to play in. Then adding a whistle in a flat key (Bb or Eb) is the next thing worth doing.
A whistle can reasonably easily be played in the key of its bell note and the keys with signatures of one less and one more sharp (or flat) - which means a D (two sharps) will also play in A major (3 sharps) and G major (one sharp) and of course the minor key and modes (7 of them - not all are very common - one is the same as the minor) with the same key signature.
Now a C whistle will play in G and F major so you only gain two extra key signatures, not 3 as suggested (you already have G)