I love most aspects of this game and have been playing it quite a bit since picking it up a couple months ago. We like to tweak games a lot for personal preference and I figured I'd put some of our house rules on here for others to review. Some of them are not our original ideas and were taken from posts on here and I'll try to give credit where it's due but if I miss some all credit goes to the original posters. Several of these ideas may be criticized but it makes for good games and several different variations (some good and some a little hit and miss).
1. To shorten the length of the game for "quickies" we subtract a random number of land tiles in various configurations to instigate interaction at earlier stages which helps eliminate anyone from sitting back and building an empire before moving into enemy territory.
2. Americans start with Democracy tech instead of Currency (gives them special abilities that have more of an impact to counteract the other civ's, ie. Russia's sacrifice for technology or Germans upgrade military, etc.).
3. Barbarian's strength is equal to lowest military ranked player (keeps villages a threat throughout entire game instead of just at the beginning). CTOP
4. Wonders are removed from the market when last player reaches next culture track level (ie. when last player hits level 2 all remaining Ancient wonders are removed and replaced with subsequent random wonders). CTOP
5. Culture tokens are collected every turn and collected again when devoted to the arts ( this works great when using fewer map tiles but for a full scale game it might make the culture track a bit too easy...we haven't tried it much with a full scale game).
6. Monarchy Government: Capital generates one culture per turn in addition to the extra when devoted to the arts (again this may only work well with the smaller tile version).
7. Engineering Tech: Every city may split hammers each turn to produce two items (speeds things up alot!)
8. Feudalism Govt: Allows combining of hammers between cities (as well as being able to harvest resources found in your other cities).
9. "Cancel a Culture Event" card cannot be subsequently cancelled by another cancel card or resource ability (rules weren't clear on this one so this is what we went with).
10. Movement in or across water requires Sailing instead of Navigation. CTOP
11. In addition to Scouts gathering from buildings/tiles bordering enemy cities, they also collect combat bonuses and Great People attributes.
12. Scouts can explore map tiles (wasn't sure about the actual rules on this).
13. In addition to the Anarchy rules already in place, the capital city also does not produce hammers (for use with Feudalism or Scout gathering), culture tokens, trade, and Great People/Wonder attributes (including Wonder's special attributes....makes Anarchy a huge disadvantage when switching governments or playing the Anarchy Culture Card).
14. Wonders may be obsoleted from the market board using resource abilities.
Like I said this is just some of our house rules so feel free to expand or comment.