I have gone through quite a few distortion pedals, and I think I am pretty good at picking out the good ones.... (of the ones that i have experience with)
Boss DS-1 - easy way to get loud, dirty distortion... you get what you pay for... if you don't want it to be as heavy, the boss super overdrive is a lot better.
Boss OD20.. I have read that some people on this forum really like this pedal, but I don't. I thought it was noisy and a pain to use. I couldn't find that balance between the volume of the amp with it off and with it on that I wanted. It just didn't fit me at all. The Boss emulators on it were good, but the others were awful in my opinion.
RAT - this one is ok. It has been many years.. but I remember thinking i like the ds-1 better. That says a lot.
Line6 POD 2.0.. this isn't a pedal, but the distortion sounds that I got out of it were great.
I recently tried out 2 newer pedals before purchasing my favorite (i will say in a minute..)
Line 6 uber metal -- OK distortion.. got a good metal tone.. too noisy compared to :
Digitech Distortion Factory... great pedal.. a lot of settings... good price.. quiet pedal...
My new pedal :
Visual Sound Jekyll and Hyde.
I just got this. I decided on it a long time ago. It is unreal. At first, it is too easy to flop aroud to totally different sounds.. and then you realize that you can get just about any level of distortion/overdrive/metal chunk out of it.
It is a double pedal (2 in one) and sounds great next to the H2O (also a visual sound pedal)
One side models the old tube screamer.. It goes from clean boost to tube screamer.. and I got tube screamer to melt your face off with the other side. If you have a shop that sells this thing.. please try it.
Hope this helps.