What is your second boost/overdrive pedal choice?

I have a Marshall BB-2 Bluesbreaker II, which has both clean boost and "blues" modes. The blues mode does a nice job of adding just a bit of dirt without messing things up.

I have one of these:
http://www.rockshop.co.nz/shop/crowther-hot-cake-overdrive-pedal.html
 
It is a bit of a legendary piece of kit. The guy who invented it played in Split Enz. Not sure if you can source them over there but if you get a chance you should demo one.

MXR M104 Distortion

I love it.

Siegmund Double Drive, Lovetone Brown Source and  Jacques fuse blower - mainly  use the Siegmund and Lovetone as I like the tones I can get from them - the Fuse blower can be a bit more extreme
Nigel
 

Mooer Green Mile.  retail $75 Can. 
I sat in a store and tried a whole bunch of overdrive pedals. The Mooer sounds like my Fender Princeton when I turn it up. I play mostly clean but when I want overdrive I want it to sound like I just turned the amp past 7 but without the volume boost. This does that perfectly.
Plus see the little toggle?  You can use that to just get a volume boost without adding any more overdrive too. Two pedals in one, very versatile.  
It's obviously trying to clone a Tube Screamer. I have a brand new tube screamer and the Mooer blows it away for Bluesy overdrive, way smoother. 
 
http://www.mooeraudio.co.uk/c/pedals
 
 

 
http://www.tomleemusic.ca/index.php/guitars/guitar-bass-effects/163784.html
 
 

Don't forget about Keely pedals. He makes several boxes that are for just clean boost.

I suspect most guitarists who've played for a while end up with a stack of dirt pedals. They seem the most "personal" effect there is, what one loves another hates. For me now it depends on what I'm looking for and the guitar and amp.

The SD-1 is good but has a bit of a mid hump that might be too much on top of a tubescreamer's mid boost. The SD-1 also compresses. Basically it's Boss's version of the tubescreamer circuit but with asymmetric clipping and a bit more transparency. Straight from the factory they're pretty versatile, cheap and have been around for ages. I much prefer them to the tubescreamer. The slight differences from the expensively modified versions don't make much difference to my ears and fingers. Though if you use humbuckers snipping the C6 capacitor off the pcb (it acts as a low pass filter which isn't really needed) can open up an SD-1 and reduce the nasal tone nicely.

The EHX Soul Food is, as Sidroe says, very good indeed. Nice buffer you can choose to use or not, great touch sensitivity at low gain settings, with a bit of compression and mid boost at higher gain. Nice blues pedal and stacks after other O/Ds or fuzzes very well. Does it sound the same as a Klon? Maybe, maybe not, but it certainly isn't $1500+ less good. The EHX OD Glove also has its fans (kind of an OCD clone).

My current personal favourites are a Dunlop mini-fuzz face immediately after the guitar. Silicon for 'buckers, germanium for single coils. Run the gain flat out, then as you back off the guitar volume the tone brightens and fuzz decreases. You can get some nice overdrive/edge of distortion touch sensitive sounds that way. Nothing responds to the guitar quite like a simple fuzzface circuit and the Dunlop ones are fine. No need to pay "boutique" prices for a circuit that uses a handful of cheap components.

Then for Tweedy Fender sounds, Lovepedal Les Lius or a clone. Everything from a bit of break up to Neil Young's "clean" tone. Run a fuzzface into it for the Young "spluttering old Deluxe about to explode" sound. For vintage Marshall-on-10 a Catalinbread DLS. Mine's a Mark 1, the current Mk3 is a little different but still impressive. Their HiWatts in a box sound pretty good as well.

Pigtonix Aria if you can find one. Diode clipping similar to the OCD/Distortion+ but with good three-band eq. Very open sound and very flexible. Pigtronix seem to have discontinued it recently for some reason.

The Distortion+ is also worth considering. Not a huge amount of volume on tap, gain starts as overdrive and gets a bit fuzzy when cranked. Has a dreadful bypass so best placed after a buffer.

Truth be told, lots of overdrives on the market are pretty similar - there are some stand-out ones but an awful lot amount to a slight modification to an SD-1/tubescreamer circuit. In the same way there are a lot of slight variations of the fuzz face, Dist+ and Big Muff out there.

bluzdog
I love my Barber Direct Drive. It's plays nicely with my TS.
 
Rocky

I'm leaning toward this pedal as well since I've been pleased with my other Barber pedals.

but this is better
 

 

also...
running the DDSS at 18v....
 
a must.
 

MakeShift
 
I just got this OD pedal a couple of months ago, at the recommendation of Herb.  I am liking the smooth overdriven tones that I get from it as well.
 
 

 
I bought this for the paint job it has.....
 
 
No, not really, I too got it at the recommendation of a player I have great respect for.  I was lamenting the tone on the Fender Tele I had bought and was considering selling. I just couldn't seem to get a decent tone that I liked. The Gibson SG I have has great tone and I had always played it with a straight cord.... no pedals. I haven't used pedals in decades, preferring the sound of the tubes in the amp for tone.  The Tele was giving me fits trying to dial in a tone I liked. 
 
So my buddy Rick read one of my posts and suggested that before I sell the Tele, to spend the $30 or so and get the Joyo Ultimate Drive and see if that would solve the tone issue. Indeed..... problem was solved as the Joyo added the right amount of sweet, smooth, distortion to let the amps work their magic in fine fashion.
 
It is the only pedal I use in my guitar signal chain.  The amps are my Mesa Boogie Studio 22w and my POD2 modeling preamp.

FWIW I finally settled on the new more compact version of the Direct Drive. I found one used and it didn't look like I could lose in that selection.

be sure to try it in 18v

The Direct Drive finally got plugged in today and it seems to fit the need very well.  
 
On another note, I also got a Digitech Luxe pedal and I really like it as well.  Reminds me of the Boss Dimension C somewhat.  It gives you the shimmer without the chorus-ey effect.