I can’t do a decent Scottish or Irish accent to save me.
My Italian and French accents are lame to the 50th power, but I have an outstanding Brit accent, a decent Indian accent and a so-so Middle Eastern accent, providing your ears aren’t native to those countries.
You?
Ayuh, i can do me a wicked good Yankee accent, a decent Southern accent, a passable British accent, and a Monty Python style “French” accent, you silly king…
not overly impressive, i know, but i can switch in and out of them on the fly, unaccented speaking, to Yankee, to British, etc…
I do a pretty good Cockney, I’m told. And I’m told that my French sounds Parisian. (A lot of that has to do with gestures and inflection as well.)
One request: for those saying they do a Southern accent, could you be more specific? I do probably a dozen of them. There are many Southern accents, all quite distinct.
I do a pretty good Indian accent, so I’m told.
Er… hang on a minute… I *am *Indian. 
I think my British isn’t too bad, and I’m listening very closely to Aussie and Scottish friends in the hope of one day picking up a bit. I could manage a little bit of a vague French, Russian or Italian accent, but break down after a few lines.
I’ve found that Australians apparently use about fifteen vowels where one will do; they say “Nawoi” (or something along those un-type-able lines) instead of a simple, direct “no”. It’s probably all this going around in the midday sun. 
I think my “default” accent is hard to classify, because we moved around a lot as a kid, but the base is close to what they call “Mid-Atlantic”, I think.
I can imitate the Florida Cracker that I used to hear all the time in my teens, and the Nawth Cackilacky (sorry, North Carolina) Southern that I lived around for a few years after getting out of college.
Actually, I’ve got a pretty good ear (my high school Spanish & French teacher said I have one of the best of any of the students she’d had), and can pick up any accent I’m around for a while.
British, Australian, French, Italian, California, Texas, Chicago. My Irish sounds remarkably like my Scottish, so I can’t really claim those. My German is laughable. My best friend does the best Indian accent I’ve ever heard; it’s the only accent she does, but I’m always jealous when I hear it because I can’t do one.
Likewise British accents 
…I manage a hybrid of a couple of them very well, and can’t do any of the others to save my life (nor any other accents at all)
Scottish and little old Jewish man.
I should be able to do an Italian but 3 years of speech classes as a kid seems to have blocked it.
I spoke with such a heavy Italian accent as a kid that I was incomprehensible outside of the immediate family.
For some reason I can’t do a good one now.
Jim
I couldn’t convincingly fake an accent (any accent!) if my life depended on it. Northerners have told me I have a cute Southern accent, but my fellow Alabamians always ask me if I’m not from around here. That’s right. I can’t even do a convincing Alabama accent.
My only good accent is Indian, it took many Bollywood movies to get it down. I can also get away with a pseudo London one.
My best are probably BBC English and Achtung-German. I can also get by in Irish, Scottish, generic Great Lakes US, coastal and inland Southern US, generic Canadian, ditto French, ditto Spanish, and Romanian-Transylvanian (which I picked up from listening to Andrei Codrescu on NPR).
Let me just say that the most botched accent, IMHO, is the Scottish accent. Yuck!
while in college studying theatre, I was pretty damn good at many dialects, tho not the actual languages.
My best may have been a brogue, which I had to learn for a part (the rest were learned/developed for fun) Ok - picture this - I am very fair skinned, and before I gave in to my inner redhead, I was a dark brunette, with very long wavy hair. All semester I used the brogue. Fortunately I had only theatre classes that semester. (This was a very common practice among the students - a non-theatre major wakling into one of our conversations would have thought we were from the UN)
OK
next semester, I’m back to talking like myself. A friend asks me what happened to my accent, wasn’t I black irish? I took it as a compliment
Now my brogue is weaker, but passable. I also retained
Frensh-Cahnaydienne
Russian/eastern european (think Boris & Natasha)
Lawn Guylandt
Niew Yawk
Joisey (which is often mistaken for brooklyn)
Southern US
Midwest US
Southern California
and I’m working on New England/Yankee - it’s wicked retahded
British Isles
My Received Pronunciation is pretty good, I must admit. I don’t really even think about that one any more. I can even speak bad Italian in RP dialect, which was hard to wrap my head around for a while. Did this one for Enchanted April in October.
London/Merton: quite good, in my opinion. Used this one for The Foreigner last spring.
Edinburgh: working on it. Not quite up to speed yet.
Dublin: fair, but needs work.
Liverpool: damn difficult to do, for me. I need a better sound sample to learn from.
Welsh: atrocious.
American
Texas: pretty convincing.
Alabama: used to have it down, but lost it.
North Carolina: not bad, but learning this one has cost me my Alabama. (That, and my roommate from Montgomery moved out.) Might audition for Crimes of the Heart in March.
Arkansas: decent.
New York/Manhattan: respectably good. Going to use this one in Coming Apart.
New York/Staten Island: worked with a guy who lived there, picked up his accent… it ain’t half bad.
Alaska/Inuit: more of a caricature accent than a real dialect.
Europe
French: inconsistent, would fool someone who wasn’t a dialect freak or linguist.
German: pretty good, given a background in the German language taught by a teacher with an authentic accent.
Russian/Moscow: used to work with two different women from Moscow, picked up their particular accent over a time. I don’t practice it much.
Asia
Vietnamese: quite good. I have several relatives-by-marriage who are from Vietnam, so it was easy to pick up.
Oceania
Australian: inconsistent. I need to get a good recording of a specific Australian accent, from a specific city, and work on that.
New Zealand: mostly I use it to imitate Richard Taylor of WETA.
I’m probably leaving some out.
do you perform in local theatre in WA, or have you done Broadway etc?
You should pop in on his thread over here.
I can do almost any New England accent. For those not from New England, yes, there is more than one. I can easily do:
Bostonian/East MA
New Hampshire
Maine
Vermont
Maine and VT are very close to each other, as is NH and Boston, but trust me, you spend enough time in NE you know the sublt differences.
I can also do a passing Irish accent. I don’t know what region of Ireland, but whatever one Colin Farrell is from, because basically I just imitate him and it sounds pretty close. I once fooled almost the entire populace of a fraternity party once. The only people who didn’t beleive I was Irish were those that already knew me, and a couple others. But then, no one at ther party was actually Irish.
Woman.
Heh. No Broadway. I’ve done some local stuff at Olympia Little Theater. It doesn’t pay, but heck, it’s fun anyhow. Learning dialects is just a hobby, it doesn’t pay the bills. 
I started studying French when I was 8, and I have a good ear for music. So, for an American, my French accent is darn good, even without practice. I also do a Yiddish accent, borrowing on my memories of conversations with my grandmother. ;j