Altan is a good choice. Old Planxty CD's are very good for real traditional stuff. They usually aren't to hard to find. Older Chieftans CD's if you want traditional.

Sounds like you're interested in the straight trad. Question is: Irish, Scots, Canadian, Capte Breton, Welsh or does it matter? Do you like the band sounds or the individual or unison trad style?

Personally, I started out (and continue) to like it all, not being ethnically committed to any one. Since you specifically asked for acoustic and authentic, I'll keep away from the fusion and more blended styles, although let me know when you're interested in branching out a bit and what you like, because there's some great stuff out there!!

So, for Irish, I recommend:

www.liveireland.com/ and select option 1: trad & folk. Free Irish music on the web - how easy or cheap can it be to try out some different sounds of established and recognized professional/pro-am musicians. This is stuff the Irish trad folks listen to. Thus, if you hear something you like, then you can follow it up.

I've got to say that in trad music, there are so many really fine musicians that although there are groups and what that I'll leave the others to recommend, I've found good success in exploring, especially from the source (e.g., go to google.ie or the like).

The BBC and Irish radio also have several radio options for traditional music. Check them out. Really great ways to find out what YOU like.

Next: try Irish shops, such as Custy's trad music in Ennis, Clarie Co or else one in Doolan or other traditional area. Here's a linke, just click through the picture then to the music area, www.custysmusic.com/. Unfortunately for them, you can sometimes identify an album and then switch over to a more accessible us outlet or amazon.com. <I didn't just say that!>

The Celtophile collections on Green Linnet are good too. Check out their site: you can list to snippets to get an idea if you like the sound.

Naturally you'll want to tune in to KALW on a Saturday at 2:00 pm to listen to Thistle & Shamrock (and the rest of the folk music line up). Ok, check out online the topic for the day and playlists from past shows, but it's a great way to hear good music that's *basically* traditional - although she does choose some "fusion" topics.

Ok, you probably wanted names to go out and just get:

Martin Hayes won best of ireland fiddle (or whatever the name is) 6 (say that again, six) years in a row: this is one truly remarkable, once-in-a-lifetime fiddler from a family of (Co. Claire) musicians. He's gone his own unique way away from strict traditional (which I love and recommend), however his first 2 cds are excellent straight trad in the nature, open-space style of Co. Clare. (eponymous and "under the moon").

He played with his dad, PJ Hayes and Tulla Ceili Band, a very good traditional group (larger group, but not of the rock style - strictly trad). Also folks like PJ Crotty.

Doolin Point: Best of Divers' Nights 1992-1999 is a cd of some fine traditional playing:
www.mustrad.org.uk/reviews/doolin.htm
which includes: Matt Molloy, Tommy Peoples, Sharon Shannon, Kevin Crawford, Donnal Clancy, Jackie Daly, Chris Droney, Andrew MacNamara, the Lahawns. (Any of these folks on their own)

I totally agree with Deux suggestions for bands.

Also Patrick Street, Lunasa - and any of the individual musicans of those bands: such as Cillian Vallely (uillian pipes) (and the cd s/ his bro Niall (concertina)); the Lahawns; John Cunningham, Kevin Burke (now Oregon, orig Ire?), Liz Carrol (Chicago) (with or without John Doyle (guitar)

Scots: now local fiddler Alasdair Fraser (a big personality and a fine fiddle) - he's got an absolutely great cd w/ Natalie Haas on cello which has that great (trad but lesser-til recently recognized) sound as was played in Master & Commander (not them, but this one's more traditional and less classical). Battlefield Band for the larger sound (try the earlier cds), Ossian for band quieter (and sweeter) - both also have songs, but the tunes parts are good. I can't think of any individual instrumentalists now.

Ok, HERE's where I miss the old Napster: why can't we list a tune or two of our faves and you can take a quick listen, then check in on what else the person likes and find gorups that way. One never gets the same having to go through the commercial route. I will state here for public: I did go and purchase CDs of the artists/music I liked and listened to. The rest I dumped and never listened to again. Word of mouth is still the best advertising, as well all well know on tribe.

Let us know what you like!

Check out www.celticgrooves.com
The guy who runs it is much more interested in spreading traditional Irish music than in making money, and has some high quality stuff.

Another name for the list: John Carty. Irish fiddle and tenor banjo. Good stuff.

Here is a local New Jersey band that I love...
www.brownejenkyn.com

they have an AWESOME self titled CD. Mostly traditional stuff..