Now we shall look through and give each Orzhov card a thought on weather to use the card, or not.
First on our list is the famous Basilica Guards! For two colorless and one plains, you can have a 1/4 defender with extort, nice for later on to block small creature rushes and extort through the game.
Next we have the rare enchantment, Blind Obedience which makes your opponents artifacts and creatures enter the battle field tapped and the extort rule. Nice to get out second turn to slow down aggro with haste and of course extort is nice.
Now we have the Dutiful Thrull, better know as, cannon fodder. And with the single swamp the can regenerate they make very good cannon fodder but for anything other than a meat shield, pick another card.
Knight of Obligation, for three and a plains he is 2/4 and vigilance and extort, pretty much a buffed Basilica Guards. He might be a game changer being able to attack and defend in the same turn but at four he might be a bit difficult to get out.
Has my favorite flavor text of the Orzhov, the Syndic of Tithes which for one and a plains he is two two with extort. A card exactly on par with the mana cost. Average card to be used in Average decks, however in Orzhov decks, he has extort so add him. "Admission is free, donations are required." -Sydic of Tithes flavor text.
The first card which requires a swamp to play, Basilica Screecher, for one mana and a swamp is one two flying and extort. Not a game breaker but a cheap flying creature for early game which has extort and can be extorted. Not an amazing card but will work fine in Orzhov decks.
Crypt Ghast, three and a swamp he is two two with extort and allows each land to be tapped for an additional swamp in addition to what they already produce. This would be good for extorting because essentially you can pay for two creatures extorting ability with one land. Other than that two two for four isn't appealing at all. Not a very noteworthy card in my opinion.
Next is Syndicate Enforce for three and a swamp he is 3/2 extort. Under par in every aspect be it ability, power, or toughness, there are better four mana creatures to get the job done.
Thrull parasite is great if your opponent is buffing his creatures and you can extort really early on him. He would be good in a control deck but usually black isn't a very controlling color.
The dreaded Alms Beast, two colorless, one plains, and one swamp he is 6/6, but there is a catch, all creatures blocked by or blocking Alms Beast gain lifelink until end of turn. It's a rare card as well and any appearance in a deck would be rare. Only would be good for sacrificing and making unblockable but for attacking and blocking other creatures, why use it?
Cartel Aristocrat for plains and swamp is 2/2 and has the ability to sacrifice another creature and Cartel Aristocrat gains protection from color of choice until end of turn. Why sacrifice a creature so save a measly 2/2? Doesn't make sense.
Deathpact Angel for three colorless, two plains and a swamp is 5/5 flying and when she dies, a 1/1 white/black cleric token is placed on the battle field with tap, three colorless, two plains and a swamp return a card named Deathpact Angel from your graveyard to the battlefield. Pretty cool ability to regenerate so you can sacrifice it over and over again. Can be a nice game breaker for any white/black deck.
Executioner's Swing, plains and black target creature that dealt damage this turn gets -5/-5 until end of turn. There are better removal spells for black out there, like murder.
High Pries of Penance is better that Executioner's Swing for a plains and a swamp, he can block a creature and destroy, not simply reduce effectiveness. But all the same, in a control deck he'd be a nice backbone but it's hard for me to se him in my deck.
Kingpin's Pet, a bland card for colorless, plains, swamp 2/2 flying extort. Run of the mill card, not extraordinary but shouldn't be easily set aside as worthless.
Merciless Eviction is a potentially devastating card, four colorless, plains, and swamp, this sorcery can exile all creatures or artifacts or enchantments or planeswalkers. This can really turn the tide of a battle at any phase. Awesome card for any control deck.
One Thousand Lashes, two colorless, one plains one swamp, this enchantment is similar to pacifism and stab wound, but more expensive and only on one creature. If you want to disable a creature take pacifism, if you want to deal damage, take stab wound. Maybe you can trade this for something.
Purge the Profane is a decent card, two colorless, one plains and one swamp for a sorcery where target opponent discards two cards and you gain two life, not a game changer but this gives you a +1 card advantage and a bit of life. You'd have to weigh this card against others to see if you really want this in your deck.
Credit to Wizards of the Coast LLC for these pictures. These pictures have been used from http://www.wizards.com/Magic/TCG/article.aspx?x=mtg/tcg/gatecrash/cig#