Here’s my list:
Any derivation of specific
Impetus
I say physical when I mean fiscal.
How about you guys?
“Apotheosis”, I stumble over that one every time. I also refuse to pronounce “gibbering” correctly, but only because I think it’s funnier the other way.
50/50 on “nuclear”
Statistics. It’s a pity, because it’s a very useful word. (And I even once worked for a few months at a government bureau of statistics).
Rural and furor. All of those Rs make my mouth squinch up. My not-from-Boston friends enjoy watching me try to say these words.
February. It sounds like I’m drunk every time I try to say it correctly, so I gave up and just started pronouncing it “feb-yoo-wary”.
Also, “Propranolol”.
Which is why god gave us Inderal. 
“Synthesis”
Which is unfortunate, since I need it on a regular basis at work.
I used to pronounce fragrant “frag rant” with a short “a”
I also used to pronounce (and spell) strategy “stragedy”, which, oddly enough, would be a great play on words to describe the current situation in Iraq…
Vicenza - the city in Italy.
It’s pronounced Va chen za (I think)
I always say something like Vin chez na
If I think too hard on how to say the word “comfortable” I can’t say it in that semi-slurred way most people do. I end up enunciating every syllable.
I always have to think before I say, and still say wrong 50%: ‘vapid’ and ‘rabid’.
why oh why do I always want to say ‘vay-pid’ and ‘ray-bid’?
I think I have finally conquered: ‘celibacy’, because in my line of work (studying religion in late antiquity) I encounter the word a whole damn lot.
“rear-wheel drive” I always sound like Elmer Fudd when I try to say that. Which is bad if you’re talking to a cop about ending up in a ditch.
For me it’s “phenomenon”… it’s not that I can’t pronounce it, it’s that I can’t help but say “doo-doo-de-doo-doot” in my head right afterwards, and it always throws me off what I was saying.
Manipulate. There’s a another, similar word that gives me the same trouble, but damned if I can remember it right now.
Sandwich
I can’t pronounce it correctly without saying it really slowly. I usually just resort to “sammich” - much easier to say.
I have a very hard time with the letter ‘r’ (rhotacism). I’ve learned ways to fake through it over the years, to the point that if I speak fast enough over it or “disguise” it somehow, most people don’t notice it (unless I stumble and stammer mildly).
However, pull out a ridiculous phrase like rural route, and I’m scwooed.
It feels so intellectually dishonest to say “feb-yoo-ary,” so I say the “R” even though it makes me sound drunk too.
However, my wife mocks me about it, and I’m pretty sure people think I’m weird for it.
Also, this is different from something I can’t say correctly, but I abbreviate words as follows:
Probably = “Probly”
I’m going to = “Ah-munna,” or even “Ah-muh”
Once it occurred to me that comfterbull actually changes the order of the letters, I have switched to com-for-tah-bull and feel much better about myself.
But I do say Febyooary and Probbly.
I sometimes slip and say something between library and libary, even though I know perfectly well which is correct.
Forward I pronounce fah-ward.
I for the life of me can’t say rivalry unless I stop and think about it first.
My wife instead of saying breakfast says something like Brekfrist for which she gets teased.
“virgin” and “version” Whichever one I’m going for, I frequently end up with the other.