I'm not a expert but I do have some input on this. Most effect units are rack mount and meant for midi or studio work... and the rest are meant to use with one hand free. just something to keep in mind.

Here's a link to Sweetwater's guitar effects units. There's a number of pedal-based effect units that will add reverb, chorus, etc. and they're not terribly expensive. Of course, you'll need a microphone to lead into the unit. These effects units aren't just distortion boxes, either. Some of them are amazingly complex and programmable. Depending on what exactly you mean by "signal processing", you may have to go to a rack unit for such things as auto tuning. Most people are just looking for a good reverb/chorus unit to add some depth to the sound. www.sweetwater.com/store/category/c307/cp39

Depends on what you really want to do. I've given up the road and gotten rid of all the big stuff, but run a couple cheap guitar boxes to fatten up the sound when I play around town doing R/B and blues with local outfits. A fairly inexpensive setup is a good mic (I use an audiotechnica clip on) and a chorus and delay pedal. You don't want too much of either, just enough too fatten it up.

I wanted a little extra "effect" as well as needing a monitor to hear what I was doing without affecting the entire stage mix. I'm using an ART Tube Preamp, running into an Alesis Nanoverb. I built a box that holds them both at an easy to reach height. The box mounts on a mic stand for easy access. To accomodate the monitor situation, I have a self powered Galaxy Hot Spot monitor that's also mounted on the same stand (using an add-on boom). This speaker allows me to monitor my effects, as well as run the house or stage monitor mix into the 2nd input. Sorry I don't have any pictures. It's cool, and at every gig we've played since I built it, there's been several musicians that have come by to check it out. It's working well for what I want and need.

My rack setup (for when I do contemporary gigs) is as follows: Rolls RM-65 line mixer Lexicon MPX-200 effects processor Korg DTR-2 rackmounted tuner It fits into a shallow 3-space SKB rack case and is very portable. Also pretty inexpensive to put together. I've always been a fan of Lexicon effects (still own an old LXP-15), but the downside of the MPX-200 is that you can't see the names of your presets--the display just shows a number. If that's an issue, the TC Electronics M-One is a comparable effects processor and shows the name of the preset on the display . . . A sax player buddy (Greg Vail) actually helped me set it up (he has a similar rack system). Since then, he has actually posted the setup and wiring specs on his website. You can check it out at www.gregvail.com Good luck!