Well, I guess it took a thread about guitars to briefly make me come out of my cyber-hybernation. Hello y'all, how have you been?
I've noticed that multi-effects pedals/processors are rather underrepresented in this thread, so I thought I'd chime in. I personally use a Digitech GSP-21 Pro as my preamp/processor and I've got absolutely everything I need in a single unit. This model is quite dated (mid 90s), but I can still get an almost unlimited amount of sounds out of it, most of which sounding pretty darn great. I'd say that the overdrives/distortions are its most lacking feature, but then again overdrives/distortions are usually the element that's most difficult to get 'just right' in about any amp setup; unless you can manage to overdrive a tube-amp by cranking the gain/volume to excessive levels (which is what real guitar distortion essentially is), chances are your distortion won't sound 100% genuine/organic anyway. And let's face it, the majority of us aren't really allowed to rock our guitar at loud concert hall levels.
In any case, for those who plan on investing in many different effects, multi-effects are by the far the best bang for your buck: plenty of great ones are available in the $150-250 price range. They basically all incorporate every effect that you can think of in a single unit: compressor, distortion, flanger, equalizer, chorus, delay, reverb, noise gate. Many of them also include a tuner and a built-in expression pedal, if you ever feel like messing around with pitches or wah-wahs. Considering that individual pedals cost around $100 on average, you'd have to invest nearly $1,000 to have access to that many effects.
You can also still use your favorite pedals along with most of these units, if your main gear already provides your 'signature sound' and you just want to occasionally tweak it with a few chorus/delays/reverbs. Many of them come with 'effect send' and 'effect return' sockets to create an effects loop, or you could just plug your pedals before your multi-effects unit. For example if you've already got your distortion set right with your pedals/amps, you could simply use the many presets of the multi-effects processor while disabling its own internal distortion.
I'd say that the main drawback of multi-effects units is that tweaking every little parameter of your chain of effects can be quite a bit more strenuous than on a regular pedalboard. With a full pedalboard you have every knob/switch readily available for adjustment, but with a multi-effects unit you usually have to navigate through a tiny digital interface. I just tested this on my own processor, and with a long chain of effects enabled I had to press 46 times on the 'right arrow' (->) to reach the last parameter; quite a pain in the ass when you simply want to reduce your 'multi-tap feedback delay' by 10 milliseconds, haha.
Anyway, they aren't exactly ideal for a live performance setup, but if you simply play at home and want to experiment with many different kinds of sounds, they certainly can provide a whole lot of fun for a relatively low price.
Here's a demo of the Digitech RP360. Guitar Center sells the basic version for $150, or with an added expression pedal for $200. It includes over 125 different effects (32 amps, 18 cabinets, 74 stompboxes). Pretty neat/diversified sounds, especially for such an affordable price:















































