I've had a lot of bad luck with recommended seeds... primarily, they are missing a specific biome. Usually, the mushroom island. So after about 2 dozen checks, I decided to use some simple mathemathetical concepts (and a few bad math jokes). Some of these went horribly wrong. Like "the neighbor of the beast", a term that me and my friends use on occasion when we encounter the series "668" while player Poker or Rook. (If you're curious, it's just an island seed; basically useless). The phone number for "Jenny" is also not enjoyable, with a huge portion of ocean.
However, I found a series that I call Countdown: 10987654321
Note that you should NOT include the final 0 in this obvious sequence: it's missing the mushroom island.
What does the Countdown have?
A variety of biomes and topography. A centrally located mushroom island (so you can landbridge to it easily). A massive snow island in the northeast corner. Deserts, plains, jungles, mountains, and three exposed lava lakes. A desert NPC town with a Blacksmith and a Wizard's Tower, and a plains NPC town. You start off next to a huge chasm that you can easily drill down to level 4, and start getting diamonds. There's even an exposed spider spawn in the center desert, with chests full of saddles. Basically, this is a perfect starter spawn, with everything.
A skeleton spawn at -159, 12, -60 and a spider spawn at -142, 16, -42. A little planning and you can connect these two spawners for massive farming.
A massive mine shaft at -140, 70, -33. Well, dig down from this point.
Mine shaft with melon seeds at 146, 6, -185. I wouldn't give this, but it took me DAYS to find melons.
In the nether, a massive nether fortress at 45, 76, -15 with at least two Blaze spawns.
A dungeon library at -168, 38, 117. Loads of bookshelves and silverfish rocks.
A portal to the end at -214, 26, 99. The dragon is, of course, upstairs. Good luck.
Does it have anything bad? Of course... one of the exposed lava lakes is actually surrounded by trees, and is easy to walk into. Two chasms are right at the water's edge and very easy to fall into. The desert NPC town has a huge, exposed underground cave beneath it that the villagers love to fall into. Clay seems to be only in the deep ocean (Notch needs to take some Geology classes). I even came upon a natural pink sheep (is that good or bad, or just odd)?