Every now and then, you feel like being artsy-fartsy (that's the technical term). There are many ways to take this challenge. Mark goes into his abstract mode and finds interesting shapes with interesting light playing over them. I tend to find a favorite model and play with shadows and light or interesting backgrounds that evoke some kind of emotional response. So when I got an email asking me to explain some simple artistic effects, that's how I responded. Wrong answer! This guy wanted some Photoshop effects. Oh, that's easier.... Now, I am not a big user of those kinds of things for a couple of reasons: they tend to be overused by some folks; and I'm a frustrated artist and usually have to work hard tot get the exact look I want. Unlike my brother who can draw, the only thing I can draw (when I stand really still) are flies. (Wait for the rimshot! "Thanks folks, I'll be here all week.")
Since I can't draw, I enjoy those effects most. Bring your photo into Photoshop, and make a duplicate the layer. You want to keep that background layer in case you want to bring in a little more color after the filter is through with its work or if you're a strong believer in non-destructive editing. Once you have two identical layers, go to the "Filter" menu and choose "Artistic." There are many choices there, but "Colored Pencil" is at the top, so start there. A menu with all the effects will appear on the right. Try clicking through the effects to get a feel for how they will affect your photos. You have several sliders on each effect that allow you to make adjustments to get just the look you want. I can give you my formulas, but play with the sliders and create your own.
I also like to take a simple black and white and use the "Graphic Pen" effect. It can create a nice simple "drawing."
There are several effects to create a painted effect. I like the results, but, since I can't draw, painting is even more foreign to me.
There are several programs out there that can help with turning a photo into something that looks like a painting or sketch. The favorite seems to be Corel Painter 11. It is a great program, and they'll let you try it before you buy it. I've seen beautiful results from several artists, and I'm blown away by the work of Fay Sirkus. Her work is top notch.
Now that the darkroom is digital, you can try all kinds of effects without ruining your original photo. I urge you to give them a try. While all of these are fun, use caution. You don't want to over use any one effect unless that is going to become your signature style.