Not all Boss (or from any builder for that matter) are all gonna be good/great/or even decent sounding sometimes. Its all up to your ears but here is what I own from Boss that rocks my socks off! 
Boss LS-2 Line Selector:
this thing is a damn swiss amry knife. 2 loops with independent volume controls, two basses, two amps, bypass loop..just about anything! I use it to keep almost all my pedals in the effects loop of my Groove Regulator AND use them independently...
Boss OC-2 Octave:
want to make just about anything REALLY FAT? here is is. all analog (also means monophonic) octaver that can do -1,-2 and your direct with volume control over each. I did the synth mod to mine for a pure squarewaveform. Mostly use it with the OCT-1 full on, direct at 9:00 and OCT-2 dimmed.
Boss FZ-2 Hyper Fuzz:
2 fuzz modes AND a dirty boost? WIN! Fuzz 1 is way more low-end friendly than 2 BUT I use the LS-2 to blend in some clean signal or run it through a T-REX Bass Juice to blend it with the Juice's very versatile tone and gain.
Boss PS-3 Digital Pitch Shifter/Delay:
I'll just list what it can do and you use your imagination. up to 2 secs of digi-delay with controllable pseudo-oscillation, single and dual-voiced detune for chorus, harmonies selectable with -1 through +1 and every semitone in between. Also can do -2 and +2 with direct thats 27 intervals! Also can use an exp for a very custom whammy, reverse pitch-shifting, harmonies with pitch shifting....AND ITS BLUE!
Roland RE-20 Space Echo:
tech a Boss but a VERY nice replication of the old school Roland RE-201 Space Echo but at 1/4 of the price, better bypass (use an isolated power supply or youll get some nasty LED oscillation noise), dedicated tap-tempo footswitch that can also do the tape-twist madness. And you can hook up an exp pedal to control rate,intensity,echo volume or the tape twist. Beat out my El Capistan!
Honorable mentions:
PN-2
DM-2
DM-3
DD-3/5/6/7
BF-2
CE-5
modded CS-3
ok thats enough
Boss LS-2 Line Selector:
this thing is a damn swiss amry knife. 2 loops with independent volume controls, two basses, two amps, bypass loop..just about anything! I use it to keep almost all my pedals in the effects loop of my Groove Regulator AND use them independently...

Boss OC-2 Octave:
want to make just about anything REALLY FAT? here is is. all analog (also means monophonic) octaver that can do -1,-2 and your direct with volume control over each. I did the synth mod to mine for a pure squarewaveform. Mostly use it with the OCT-1 full on, direct at 9:00 and OCT-2 dimmed.
Boss FZ-2 Hyper Fuzz:
2 fuzz modes AND a dirty boost? WIN! Fuzz 1 is way more low-end friendly than 2 BUT I use the LS-2 to blend in some clean signal or run it through a T-REX Bass Juice to blend it with the Juice's very versatile tone and gain.
Boss PS-3 Digital Pitch Shifter/Delay:
I'll just list what it can do and you use your imagination. up to 2 secs of digi-delay with controllable pseudo-oscillation, single and dual-voiced detune for chorus, harmonies selectable with -1 through +1 and every semitone in between. Also can do -2 and +2 with direct thats 27 intervals! Also can use an exp for a very custom whammy, reverse pitch-shifting, harmonies with pitch shifting....AND ITS BLUE!

Roland RE-20 Space Echo:
tech a Boss but a VERY nice replication of the old school Roland RE-201 Space Echo but at 1/4 of the price, better bypass (use an isolated power supply or youll get some nasty LED oscillation noise), dedicated tap-tempo footswitch that can also do the tape-twist madness. And you can hook up an exp pedal to control rate,intensity,echo volume or the tape twist. Beat out my El Capistan!
Honorable mentions:
PN-2
DM-2
DM-3
DD-3/5/6/7
BF-2
CE-5
modded CS-3
ok thats enough