Refuge Cycle and this Cycle have now been ousted by the Gate Cycle in Return to Ravnica:

Golgari Guildgate
Azorius Guildgate
Rakdos Guildgate
Selesnya Guildgate
Izzet Guildgate

1. These are 'budget' lands- there are better lands, so if you're looking at these, you want cheap cards.
Common is better than Uncommon for getting Cheap cards. Actually have a great chance of picking up a full 40 set for less than $5. $6 at the absolute most, if someone really charges you 15c each, but that's kind of jerky. Commons should be: 'you can have a huge pile of them, plus 10 crap rares at a dollar a rare'.

2. They have a relevant subtype- 'Gate'- that can make some other cards a lot better/reasonable. I don't think this new 'Gate' thing will be hugely important outside of Limited, even considering the name of the set 'Gatecrash', but it does mean that budget decks with budget synergies will be ... (see all)