Chaos Wins!

Urza's Block Constructed has changed significantly from the vision of WOTC back when the set was released in the late 90's. A series of bannings to some of the more ridiculous cards like Time Spiral or Gaea's Cradle tempered the power level of the block quite a bit. That still didn't stop some powerful combos from emerging, especially with the "free" mechanic that allowed players to cast spells and then untap lands associated with them. Not nearly as powerful when comboed with the likes of the Cradle or Tolarian Academy. But still good in a vacuum.

Note the robust ban list that exists for this block. The longest next to Mirrodin Block Constructed.

What we have below are two decks that survived the bannings or more appropriately, became viable because of them. In the true spirit of the block the combo deck wasn't removed completely. Naturally to counter that is a permission deck. They square off against each other in a battle of resources.

Opal-plenish

Spells

2 Turnabout
4 Frantic Search
4 Attunement
4 Opposition
4 Confiscate
4 Lilting Refrain
4 Opalescence
2 Worship
4 Replenish
4 Disenchant

Land

9 Island
7 Plains
4 Faerie Conclave
4 Forbidding Watchtower

Sideboard

2 Turnabout
2 Defense Grid
3 Quash
2 Scour
3 Energy Field
3 Annul

This is an interesting combo oriented deck that focuses on filling up your graveyard with enchantments (including Opalesence) and then dumping them all onto the battlefield with a well timed Replenish. Barring some kind of wrath effect the following turn by your opponent, that usually meant game over as you locked everything down with Opposition and then just ran your opponent over with an army of creature/enchantments.

The combo is pretty straightforward. The deck uses the ridiculously ban worthy (yet it survived the bannings) frantic search and Attunement to find Replenish all the while helping the cause by dumping pricey enchantments into the graveyard including Opalescence. Lilting Refrain helps protect the combo from going off against the likes of enemy permission magic. Simply fill the yard, Replenish everything back into play, and win shortly after.

Con-Troll

Creatures

4 Yavimaya Elder
4 Albino Troll
3 Acridian
2 Palinchron

Spells

3 Treachery
4 Rewind
2 Power Sink
1 Miscalculation
2 Hush
3 Rescind
3 Stroke of Genius
4 Powder Keg

Land

9 Island
2 Faerie Conclave
4 Treetop Village
10 Forest

Sideboard

2 Simian Grunts
2 Rebuild
4 Annul
2 Turnabout
3 Arcane Laboratory
2 Quash

Con-Troll is a more traditional "control" deck featuring cheap efficient creatures backed by permission magic and board sweep effects. The deck features card advantage in the form of Yavimaya Elder and Stroke of Genius and hopes to draw into enough counters to overwhelm the opponent. Powder Keg deals with swarm decks. Acridian and Albino Troll are cheap ways to stop an early rush and also finish the game once card advantage is firmly established.

Both the above decks are good additions to your block constructed collection. They capture the theme of the day, use a lot of the unique mechanics introduced back then like Echo and the "Free" spells but also don't win in 2 turns like the Academy decks prevalent before a ban cycle kicked them out of tourney play and into the confines of some power trippers kitchen table.