|Your photos look great!
A couple of things I would recommend you try out are:
1) Neatimage (a.k.a - the photographers jesus - please excuse my religiously inappropriate lingo, especially if you are religious, because I have NOTHING against anyone being religious, or against any religions.) this handy dandy utility gets rid of extra noise in your pictures, and does it very secretly, and very well! It is a seperate program from Photoshop of whatever you use, so you'll have to download it!
2) Hue/Saturation - you can find this in your current image manipulation program, i recommend it for your sunset/sunrise photos as you can give an extra kick to your colors
3) Levels - find in your current program, can bring out the nature contrasts in a picture, absolutely a must for b&w, but still important for color)
4) Unsharp Mask - you probably read about this one, it's important, use it, but use it subtlely, many people overuse this filter and make there photos worse!
Those are the basics! Remember, being subtle is the key! Make it look natural!