First off, let me tell you something very important: no guitarist, in the history of the world, has ever needed a 100W amp. Tube amps sound the best when they are cranked, and you will never be in the situation where you can crank a 100W amp. Even if you're playing a giant football stadium, you won't need a 100W amp. If a 30W amp can't fill the venue, you're getting mic'd... plain and simple. Once that microphone goes down, your volume has to follow.
So don't waste your money on a bunch of extra wattage. It's really nothing more than a marketing ploy for the ignorant. Most high-end amp manufacturers have matured and dropped away from the BS that was 1980's amp marketing and have returned to making high-quality, low-wattage amps... Marshall hasn't. The lowest wattage tube amp they make that isn't a reissue of a 50 year old Jim Marshall design is 50W, which is still more power than most guitarists will ever really need.
All those Zeppelin, Sabbath, Cream, Hendrix, Blue Cheer, etc etc albums were recorded with amps in the 5-15W range. If you really want the best sound possible, find yourself a high-quality amp in the 20-30W range... like the Vox AC30 or the Laney LH20. The ONLY reason to buy anything more powerful than 50W is if a lower wattage version does not exist or if you need to feel like you've got a big penis.
Anyways, different distortion pedals react differently with different amps. Are you going to use a combination of pedal and amp distortion (like Stevie Ray Vaughn) or pull all your distortion from a box (like Joe Satriani)? Both are perfectly valid approaches, but you wouldn't use the same pedal for each situation. If you're just looking to give your amp an extra kick in the *** to hit the preamp harder, you want something like the Ibanez Tube Screamer (or the Maxon OD9, a VERY nice replica of the originals... closer than what Ibanez makes today actually). If you want all your crunch from the pedal while keeping the amp really clean, you want something with a little more bite, like the Boss DS-1 or the ProCo Rat.
I recommend that you try out different distortion pedals while you're shopping for your new amp. You should buy an amp that sounds good on its own too. You shouldn't be looking to pedals to save a boring sound. They are meant to enhance your sound, not define it.