When it comes to distortion I prefer to simply use the gain channel of a decent all tube amp. Digital distortion can't compare in my opinion. That being said, if you've got the cash there are a handful of pedals that run tubes to give them a more natural, warm tone. I used a Radial Tonebone Hot British for a while and it was good for a Marshall-esque high gain. My personal favoruite (if you can find one) is the Soldano Supercharger. That pedal is a beast, but sadly isn't in production anymore. If you're looking to simply get a bit more gain out of an amp you already like the tone of I'd recomend a Fulltone Full-Drive 2.
Something a lot of people don't realise with the mass produced pedals is that when they're turned off they run your signal through a buffer. So so more pedals you run your guitar through the weaker the original tone of your guitar will get. You won't notice it with just a handful of pedals, but you will once you get a serious pedal board going. You can get true bypass pedals, but they'll cost you a fair bit more.
