I haven't played DOTA, though you can see DOTA games everywhere on B.net. I hear it's similar to the old Aeon of Strife maps for SC (which were said to resemble Dynasty Warriors games).
One of my favorites was Science & Industry (HL1 mod). For those of you who haven't played it, it's like this:
Two teams, each with identical bases on a symmetrical map. The teams are not different at all. The objective is to have the most money by the end of a set time limit for each round (I believe it's 30 minutes).
To accomplish this, you have to have scientists generate money for you. Each time starts with 3 of these little guys. The trick here is to kill (preferably, to capture) the opposing team's scientists. You capture them by hitting them with your briefcase weapon and carrying them back to your human resources department in your base.
Another benefit to scientists is that they research new technology for you. The more you have, the faster it goes, of course. Same with money. Scientists can research new weapons, bionic implants, faster respawn, etc. Needless to say, you'll need these to compete with the enemy team as they try to kill you (to reduce your team's money) and take your scientists.
Much of the game is decided in the research periods, which occur for a team when it has finished researching its current technology. In these research periods, team members have to vote on the next item to research. Whichever item gets the most votes will be researched next, and it continues until the research is done.
So it continues like this, with both teams gradually building up technology. There are some of your classic Half-Life weapons (Tau Cannon, Crossbow), some stranger ones (Flesh-Eating Virus), and relatively original or standard ones (Machine Gun, Akimbo Uzis).