I've noticed that I had to make a few similar changes for every GOG game, so in case someone has the same issues as me - I thought I'd post them. All suggestions require you to open your Program Files GOG.com Game Game.conf file and find the relevant section or line.
First off - the sound quality. It may be scratchy or just not quite as good as it could be. Under the [mixer] section change the output to "OUTPUT=44100". This raise the overall sound quality. There are also individual rates such as sbrate= and adlibrate=, I set everything to 44100. It gives you the best quality with next to no hit on performance. Even on my low end PCs it doesn't affect the speed.
Second - speed. If the speed is not up to snuff, adjust the cycles. Most games will either use cycles=auto to have dosbox adjust for you or cycles=max to get the most speed you can for heavier games. Swap between the two if you have issues, but so far with GOG's catalogue you don't need an exact number. Stick with those two. However I did notice some games have frameskip set to "1". If you have a fast PC, set this to 0. It will smooth things out for you.
Third - LCD owners. I find dosbox can be a bit picky with these panels. The method that almost always works for me is to set the following
Output=ddraw
Fullresolution=1920x1200 (insert your native max resolution here, whatever it may be)
Scaler=none
This will stretch/pillarbox the game depending on the resolution requested. You can also set aspect=true for some aspect correction. If you want to force the game to stretch on a 16:10 monitor, use a 4:3 resolution like 1600x1200 or 1024x768 and the game will stretch width-wise every time. Helps if the game really wants borders (Redneck Rampage I believe is one of them)
Vista users - Do not use OUTPUT=Surface. I'm pretty sure no GOG.com games do by default, but don't change it. Surface causes some strange colours when it goes into fullscreen mode. Use DDraw instead, as it actually improves the performance for Vista. At least it does for me, it makes using alt-enter much quick for one thing.
To run the game's setup program (to change redneck rampage's controls) Drag the setup.exe onto dosbox.exe and everything will automount and run. That way you can add 'wasd' controls or change the music/resolution settings to suit your needs.

you know, i didn't even realize that GOG was using dosbox for their releases. i wonder if GOG is working with the dosbox developers to optimize dosbox for each game, like how steam did for the X-COM games.

Great and useful post. Should be stiky-ed!

Yeah... I mean for every people which would need it and who haven't seen it. Like the Game Mods threads are stickied. It would also avoid useless help threads :)

I thought you wanted a scaler? It helps games look better at higher resolutions; yes, the default is rather worthless, but I use advmame2x on Earthworm Jim at 1280x800 and it looks great.
Also, to improve sound for dosbox games that use Midi(I'm not sure if there are any now, but I'm sure we'll get some), one thing you can do is use Timidity++. Follow the instructions here (yes, I know its for scummvm, but the basic setup is required to use timidity for anything). Ignore the line about setting scumm to use Midi(obviously) and load up the setup program for the game you want to play and set the option to general MIDI. The game should now send its MIDI to Timidity++. Note that this will be a bit slower than in DOSBOX midi or SB emulation, but I can play Wing Commander III in Dosbox with TImidity on a 1.8 ghz AMD sempron 3200+ with only some very minor stuttering.

A scaler only helps with lower resolutions. If you scale to your native, why would you add another scaler on top of that? For me DDraw produces a crystal clear image at 1920x1200 without any need for extra scalers.

XCOM and XCOM Terror From the Deep have been available in WIndows Optimized versions for free from HotU for years.

Firstly, the windows optimized versions, like many such versions from the early windows era, are harder to run on modern systems than the original DOS versions are when wrapped in DOSbox.
Secondly, X-COM is still being sold buy 2K, and therefore the game is not abandonware. Please don't encourage piracy.

They both work fine in XP, don't know about Vista.

The 'scalar' field in the DOSBox .ini is also where you get specify graphics filters, which are the emulation equivalent of anti-aliasing. Supereagle, hq2x, hq3x, 2xsai, etc are all filters. They enlarge the image, yes, but they also clean it up!
Here is the author's page for the hq3x filter included with DOSBox which demonstrates the function of the hq3x filter quite effectively, although you really need to see it in action to really appreciate it. There are also examples of hq2x and hq4x on his site.
As you can see, if you prefer the antialiased image the quality difference is enormous. You're not just scaling the image, you're also cleaning it up. It has helped with console game emulation for a decade now in the form of the classic Supereagle filter, and of course mame has benefited from the advmame filters. hq2x is a worthy successor to supereagle, and hq3x and hq4x take things to the next level.
Without an extremely high resolution monitor you can't even take advantage of hq4x, and instead most people are better served by hq3x (or hq2x in the case of 640x480 games).
All that said, great thread!

Good tips, but I wanted to make a note of something.
I have a 16:10 monitor, and my experience is a little different.
I haven't tried the "aspect=true" setting myself, but to get pillarboxing what I did was set the fullresolution to a 4:3 resolution. I have an ATI card, and ATI's last few driver versions support GPU scaling while maintaining the aspect ratio (where the video card scales the image)... prior to this, my monitor always stretched 4:3 resolutions. I'm of the opinion that (just like movies) games are best enjoyed in the correct aspect ratio (e.g. not stretched for older games), so I really hate stretching. Using GPU scaling has the added benefit of making Windows games with no widescreen support pillarbox, in addition to doing it for DOSBox.
nVidia cards and drivers may work differently, and using "aspect=true" may negate all of this. It could be that the "aspect=true" setting was included in DOSBox to allow pillarboxing prior to ATI's driver support (I believe nVidia has had the feature in its drivers for a while now). I'll try both ways when I get a chance and see if I can get more detail on this.

I'd like to point out that cycles=auto is not actually much different from cycles=max. It runs the emulator at low cycles for games running in real mode and at max cycles (identical to cycles=max) for protected mode. Personally, I find manual fine-tuning of cycles to produce better results than autodetection.

Surface output is the slowest one and causes graphic glitches in some games. DDraw is the fastest, but the images appear to lose definition when using this output mode.
Personal suggestion? Overlay .

True, but keep in mind that certain exceptionally resource-demanding titles might require the lower sampling rate to reduce CPU load (think: Quake, Duke Nukem 3D, System Shock Enchanced CD or X-Com: Apocalypse).

So where do I go to adjust these settings? I don't see any options menu in Dosbox, just a command prompt.

bump
anyone?