Brainstorming help!

There are many directions you could go with something like this.

Economic:
You could have straight-up land-based resource generation, Magic: The Gathering (or if you prefer, Settlers) style. Each land type might provide a different resource, or mix of resources, which in turn are used (in aggregate) to purchase various things in the game appropriate for that sort of resource. Hills might produce clay, bricks, ore, coal, gold, or simply brown mana, forests produce wood/green mana, swamps produce oil/souls/black mana, etc.

You can shake this up a bit by making some tiles benefit from being next to OTHER tiles; perhaps for a sorcerer, a single large swamp is a better source of mana than a bunch of little swamps. Maybe each swamp generates X Black Mana for the total size of the swamp. So:

1 swamp = 1 mana
2 swamps = 4 mana (2x2)
3 swamps = 9 mana (3x3)
etc.

Another geometric pattern: swamps work on a sliding scale, each one adding the total number of swamps. So the first one is worth 1, the next is 2 (total 3), the third is 3 (total 6), the fourth is four (total 10), and so on. This kind of scaling is a much easier to control, but more mathy.

Piling tiles on top of one another is another cool direction to explore -- perhaps some land types aren't worth much unless they're developed, but the development tiles are only able to be put on a certain kind of terrain. Mines on mountains, cities/mage towers/farms on fields, etc. This might be really fun because the players will start out with a mostly barren countryside and end up with a bustling nation-state.

Military:
Again, you could have simple 1:1 resource generation, but the resource is military units. Each forest produces one elven archer, each hill produces a hobbit (sorry, halfling), each swamp produces an orc/zombie/ghoul/wraith, etc. This might be per turn, or every X turns, or it might be the total maximum supported army size, in which case you'll need to create another means for players to purchase armies.

Another option is providing a stat buff to existing army units, depending on the scale of your combat. A really general example: each hill is +1 fighting power (from mining higher quality armor and swords). More specific: each forest gives your archers +1 range in their bows. You could have players allocate stat buff points -- with this example, perhaps 10 forests give you 10 green cubes that you place on a card, allocated between defense, offense, archer range, archer reload speed, whatever. This can be as general or as granular as you want, but the cool thing is that players can choose to make really specific armies based on the layout of their countries. Balancing would be hell though.

Political:
Each terrain type might support a different constituency, with varying needs that must be met by any good ruler. Dwarves (mountains) want gold, elves (forests) want... to be left alone, maybe? Orcs (swamps), of course, want power.

A player might count which terrain type holds the majority of his country, and advance the interests of that group in order to win, or simply receive an improved ability to win according to that group's ideals. If you have more swamps than any other terrain, your armies are stronger; if you have more forests, you're better at magic.

Anyway, just some random thoughts to get you started. Good luck!