Question for all from a relative newbie: what would you recommend as the most important keys to have after D? What whistle (or whistles) do you use most outside of old faithful?
Definitely a C whistle. With a C and a D whistle you will be able to play just about anything that is likelly to be played at a session! 
Slán,
Anders
It really depends on who you play with. I rarely use other keyed whistles at sessions unless there is a singer and the singer I usually play with sings a lot of stuff in F and Bb so I tend to use my Low F a lot.
A C whistle is a good choice for a different key though it is not too different from a D, but gives you a more mellow sound. Eb is also a good choice as there a lot of recordings on Eb Flutes and Whistles plus you never know when you could find yourself in an Eb session, but I have never actually seen or been to one. A friend of mine says he plays at one in Co. Tyrone, but I have never been.
Depends on what you’re using it for…a C whistle will come in handy at sessions from time to time (it’s the “Julia Delaney whistle”), but if you’re playing on your own, it’s up to what sound you like. I think Bb whistles are particularly nice–they still have some high whistle mojo, but they’re significantly mellower than a D whistle.
Don’t forget Eb, my favorite whistle is in Eb, it really flows and sounds cheerfull. Many recordings are in Eb, too.
You know, it all comes down to this: you’ll eventually buy them all, so why not order all keys at the same time and save time?
Bb, C, Eb, in that order
I find C the most useful when playing with others. Bb is kind to the ears. The Eb has a wonderfully bright sound.
The good news is that the Generation Bb and Eb whistles are very low cost and usually sound great.
Thanks everyone for your input! I’ve just ordered a Bb (and have Eb & C on my horizon for next month).
After just purchasing one of Paul Busman’s beautiful wooden whistles (a D in an Australian wood called Minniritchie), I have been bitten by the wooden whistle bug. Perhaps it’s due to my harp tendencies?
You were right. I am going to end up with one in every key… oh, who am I kidding? It’ll be more like 5 in every key.
Thanks, as always for your help!
CelticHarpie,
First, thank you for posting this question. As a relative newbie myself, I have been wondering the same thing.
Second, I too have been “bitten” by the wooden whistle bug. I just purchased the Paul Busman D in Bendee that he made. I guess you could say that your whistle and my whistle are related (at least in a timber sense). I was considering the minniritchie as well, so I have to ask: one, is it as beautiful in person at it looked in the pictures, and, two, more importantly, how does it sound?
Michael
Good to ‘see’ you again CelticHarpie!
I had been wondering this as well; I have 2 D’s and a C.
My future plans (already) … are a Gen Bb (which should ‘play nicely’ with Eb and F), G (maybe a Becker whistle? - although I noticed no one mentioned G…), and a Low D (I’m thinking maybe a Tipple flute here - had concidered the Dixon Duo, but from mostly poor reviews have reconcidered that one).
Another thing besides key is how the character/sound of the whistles change with the keys. My ears really like the low D’s… 
My favorite key to play in on piano is Eb… so maybe I’ll pickup one of those as well (or just hit the xpose key on my synth…)
From what I’ve read here, and listened to on YouTube - I like the sound of these the Gen and Tipple. Both are well thought of here. Still not sure if I want a low D whistle AND a flute…?
But, like you said, get one (or more) of each , that way you’ll be ready for anything 
Don’t forget about an A. You can play tunes in D that go below the bottom D note.
Angelo
It’s beautiful, both in sound and wood. I just got it on Monday and haven’t had the chance to play much (plus there’s the dreaded breaking in phase). I am looking forward to it being broken in enough to play for longer periods of time.
I do love the quality of the tone. As I’m relatively new to serious playing (but a woodwind player from way back), I’m enjoying how it responds to cuts and slides (the only ornamentation I’m fairly competent on at the moment). I think I read a review that said the sound of the whistle “screams Eire” and I have to agree with that particular assessment!
So my whistle collection is now:
Feadog in D
Burke Brass Session in D
Busman Minniritchie in D
Reyburn Wide-Bore Low D
and a Thin Weasel in Cocobolo in Bb (on its way to me as we speak).
I just realized that when the newest whistle arrives, I will have surpassed my harp collection in number!
Collecting is fun, innit?
Alright, I received my Bb Thin Weasel on Saturday and have been getting acquainted.
Adrian, you were correct. The Bb is very mellow. It’s taking a bit of time to get used to the sound (and to the difference in air requirements), but I’m enjoying it.
Of course now I’m thinking about an Eb and a C.
Dangerous, this whistle business. Dangerous indeed.
A lot of people seem to really like Bb whistles… I definitely need to get myself one.
+1 here too.
I read that again - and thought it struck a ‘funny ‘cord’’ - related in timber … and timbre?
I wooden know…
TravM63,
Ha! I “wooden know” either. When I wrote that line, I honestly had no pun in mind, but now that you point it out… 
CelticHarpie, I’m glad that you are enjoying the Thin Weasel. I’ve heard the are very similar to the Busmans (it is not surprising particularly since Mr. Schultz was Mr. Busman’s mentor).
You’re absolutely right - this whistle business is dangerous. I’ve already got the Busman, a Hudson winds, and a Sindt in D (all fantastic whistles in my humble opinion, and each with a beauty and sound all their own). I’m not done yet (heaven help me). I’ve got an Abell D/C set on order and hopefully will be ready soon (it’s been nearly seven months 
), and I already am thinking about ordering a Bb from him. I swore that WhOA wasn’t real. WhOA is I and all those who doubt it. I’ve got it and got it BAD!
Aren’t whistles great!
Would an A or G also be useful? I do not have the occasion to session much, but have ample opportunities to play with guitar and fiddle players.