I gotta tell you, I'm in agreement, no one reel is great for everything; but, I think you could get away with a Penn GS - ie 535GS; it's a graphite non-level wind conventional reel, that's made for casting. This might be a little on the heavy side for fluke, but wouldn't be too far off and still has the line capacity for any striper / bluefish out there or anything else in that range. The gear ratio is very high - between models it's 6.1:1 - 5.3:1 and line capacity is between 400 of 15 and 600 of 20. $130 at West Marine. I've never owned this reel, but it's a Penn and is probably rock solid. Throw it on a 10-20 lb class 7 ft pole w/ 20 lb mono and you'd be all set for boat stripers/blues/fluke - w/ 30 lb it'd be good even for cod.
The reason I'm pushing you toward conventional is that they work much better w/ heavy weights and deeper water - this is almost impossible w/ a Spinning reel. Also, I'm assuming every now and then you'll want to cast, hence the casting conventional reel. If you wanted one reel for everything, that's the only way I can see it working.
Spinning reels are great for anything other than water over 50 ft. If you are going to be in shallow waters only and don't like casting conventionals (bait-casters) - I'd say go with a Penn live-liner (the larger of the two they make - 5600L). The live-liner is a free-spooling spinning reel, so it's perfect for bait w/ stripers and anything else in that range. Good for 20 lb class, but nothing heavier. I have one and it quickly became my favorite - has worked flawlessly so far, but can only claim a few months of use. That reel was $145 at WalMart.
If you were going w/ two reels, I'd really say one spinning and one conventional - covers more ground that way.. but, the possibilities are endless - really depends how much you want to spend and what type of fishing you'll be doing.