After the used outboard thread, I've considered what boat would be suitable for the local "lake". It is a man made flood control resivour, 20' deep, 6x1 mile, and a 25 hp limit. It would also see use in the larger finger lakes. Use is general recreation and possible light fishing secondary.
Any aluminum with a deep v hull. Hold out for a flat floor. Maybe a pontoon, but I don't like pontoon boats and 25hp won't push one very fast.
Jonboats (what toyman posted) are a good option, but they'll get thrown around pretty easy. Not an issue on your small "lake", but it might be an issue on the finger lakes.
Used.
http://binghamton.craigslist.org/boa/5655342028.html
http://ithaca.craigslist.org/boa/5643144677.html
Not aluminum or a Deep V, but check out the engine to see if it is a Mercury design or a Chrysler design. If it is a Chrysler, then run--if not, take the HP sticker off so no one knows what it really is: http://ithaca.craigslist.org/boa/5634861019.html
6x1 miles you will not get too much "fetch" but at 20 feet deep, those waves are going to be "square" like they get on lake Okeechobee. As you are limited to 25hp, you want a light weight hull that is easily pushed up onto a plane. The Jon boat is a good idea. A deep V, like suggested, probably will not get up onto plane at 25hp.. you need a flat or a flattish bottom for most of it's length to do that with so little power.
Want the most fun you can get at 10hp?
If you feel like making a project out of it and want to build your own boat, then with a 25HP limit and not considering a sailboat, I would recommend Marissa.
Sailboat.
Master the fine art of going nowhere, slowly, at great expense. 
But honestly, I've had a couple of sailboats and really enjoyed them. It's a more engaging way to travel than motoring about making noise.
The best boat is one you don't own.
Pontoon boats come in all sizes. I've been coveting an old Hobie with a bent mast and no tramp. Make a trampoline out of wood or glass, two bucket seats and a 15hp and I think it would go well.
Toyman01 wrote:
I agree with this in general. The modified jon boats with the slight v bow and tunnel hull get up on plane with little motivation and don't hit as rough in choppy conditions. You can always add a couple molded seats with padding to increase cruising comfort over the metal benches. Just avoid the ones with the square bow. They'll loosen your fillings in the kind of waves you're gonna see.
Most of those v-bow boats I've looked at in my area seem to hold their value pretty well. That's a benefit when selling, but makes buy-in a little harder.
Something else to consider is an older V-hull aluminum or fiberglass utility boat with an under-25 outboard. It won't plane as quick (or at all, depending on the combination) but they make good knockaround boats and can usually be found cheap. Stuff like this, usually in 12-14':
Since we have the serious recommendations out of the way, can we start recommending 2500hp Elco PT boats? 
Yeah, if you can keep your foot out if it and under 25 mph.
Jon boats are a fantastic and cheap way of getting on the water, but it doesn't take much chop to make them into a disc-herniating machine. The more modern semi-v jons like pictured above do slightly better, but not much.
I would personally go 14-16' aluminum V with a fabbed plywood floor for easy walking. For the finger lakes, consider a console/remote. Getting your weight forward is helpful on gusty days. Our rental boats here (14' grummans and springboks with johnson 9.9s) are great, but unless you have at least some weight up front a good gust can alter your direction rather dramatically.
For examples of what I'm talking about, do an image search for "crestliner 1450". I'm not specifically suggesting getting a crestliner 1450, its just one example I knew of to demonstrate my suggestion.
Tiller version
Side console version
If you're concerned about weather on the lakes (which I am) you might consider a runabout. Old v-hull fiberglass examples are a dime a dozen. The hood and windshield make shore docking a bit of a pain. Ok, a LOT of a pain. I had one for years and finally tripped on the windshield sending me flying onto the floor and turning the windshield into plastic toothpicks.
Next step up would be something like a bowrider with a walk-through windshield. Best of both. Close the windshield and enjoy protection from the elements, open in it for easy walk through and front entry/exit.
Big caveat there is they are usually a 16' and up boat before they are made as bowriders. 20 hp on most bowriders is going to be painfully slow. Shortest bowrider I really know of is my Glassmaster 15', and it probably needs 40-50 hp to plane.
Like this:
Can you define general recreation?
914Driver wrote: Pontoon boats come in all sizes. I've been coveting an old Hobie with a bent mast and no tramp. Make a trampoline out of wood or glass, two bucket seats and a 15hp and I think it would go well.
Is that an original idea or is that something that people do? Because that sounds fun and easy.
Appleseed wrote: The best boat is one you don't own.
It's the one your friend or neighbor owns.
WOW Really Paul? wrote: Since we have the serious recommendations out of the way, can we start recommending 2500hp Elco PT boats?
Pretty damned tough to find.
Find one of these, keep it in decent shape, re-sell any time for what you paid if not more.
Easily pushed by 25hp, stable, well made, light weight, nice open design. They pound a bit in chop, but no worse than anything else you are considering.
I could always go back to looking for a square stern canoe and a 5 hp outboard.
I am going to push them some.. but if you do not building.. Chesapeake Light Craft does a good job with their kits and plans. I happen to like their Peeler Skiff
If you can wait a couple of months.. wait till fall, that is when people sell their boats for cheap. Come down to some place like the Atlantic City area where small boats are cheap and people are tired of paying for them
Woody wrote: Is that an original idea or is that something that people do? Because that sounds fun and easy.
I saw a kit once, it was an fiberglass deck with a built in bench seat and outboard mount. It screwed onto a Hobie but too pricey for me. Why not GRM it?
If you don't mind a little work, Runabouts are plentiful and cheap. Paid $700 for this, ran it a year and made a little when it sold.
Agree with Curtis. An aluminum boat is all but indestructible. You can ignore it for years with it outside sitting upside down on saw horses, then go pick it up and throw it in the water.
FIL has a heavy old ~12-14' Deep V hull one with a ~10 hp outboard. Two people can carry the boat itself down to the water (barely), and it can be carried in the bed of the truck. Same the outboard and fuel tank. More than enough power to come up onto plane and zip around. Not a boat you want to be in foul weather on, but in general you don't ever want to be in foul weather. It's enough speed to zip into shore when storm clouds boil up.
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