I've grown much, much more accustomed to the style of play in Dominion and frankly I'm starting to enjoy it. "Herding cats" speaks to both game modes and frankly, sometimes you just queue with bads. It happens. But being really good and knowing how to Dominion goes a long way toward making those bads less debilitating.
I pretty much exclusively play Rammus on the Crystal Scar. I've said this before, but he's amazing on that map. Powerball gives him mobility, which is just so crucial here; the fact that his other abilities are just amazing on their own really puts him over the edge.
Start with: Heart of Gold, Boots of Speed, 5x Health Potions
Summoner Spells: Heal*, Flash
*I've come to really like Heal on Dominion and especially on Rammus; with DBC and solid gear, he's nearly impossible to punch through, and Heal just makes that task even greater for your opponents. Plus, for me, Rammus is all about having "buttons"; you build Randuin's on him, Odyn's Veil, and so on, and he just ends up with a ton of emergency switches to hit in big desperate group fights. Powerball to disrupt! DBC to become tougher! Taunt to...taunt! Tremors to AoE! Randuin's to disrupt! Odyn's to AoE! And, of course, Heal to heal. Built right he's just a font of tankiness and I think Heal is part of that. Plus, having Heal can very easily swing the battle for the Windmill at the start of the game in your favor, which I think is kind of huge.
Flash is self explanatory. It's fucking Flash.
Runes: Magic Pen Marks, Flat Armor Seals, MR Per Level Glyphs, and Movement Speed Quints
Masteries: 0/21/9 (standard tank build)
Skin: NINJA RAMMUS
This is actually kind of a lie. I will often max out Powerball before DBC, but I usually get DBC to 3 or 4 before I hold off on pumping it up.
Basically, you're a mobile tanking wrecking crew. Powerball and movement speed shrines, along with your Boots and Quints, let you tear around the map really, really, really fucking fast, the upside to Powerball being disruption on contact if you time it correctly. (E.g. don't Powerball too early, you want to literally roll up onto a fight every time.) Rammus, like a lot of tanks, has some squishiness early in the game before items, but his abilities protect him very well and with healing shrines and potions you should be able to stay in the arena without having to port too much.
First port: You'll want to finish your Boots (Mercury Treads all day long, unless the team is AD heavy, in which case Tabi boots all day long) and pick up Cloth Armor.
Second port: Ideally, finishing Randuin's, but more often than not you'll just buy Warden armor.
Third port: Likely finishing Randuin's. If you can get a Negatron Cloak, do. (Again, assuming a balanced team.)
Fourth port: Catalyst. And go from there.
I like to have a balance of defensive stats on Rammus even though DBC lets him "cheat" slightly. You can't rely on your steroid to keep you alive all the time. So for me, Rammus' core on Dominion should be Veil, Omen, and Mercury Treads; after that, it's up to you. I like a good old Sunfire Cape if I'm facing a heavier balance of AD to AP, and an Abyssal Scepter if the reverse is true. Against ALL AD, rush Randuin's and immediately go for Thornmail. (Duh.) After that health items.
I've come to love the fuck out of Shyvana on Treeline. She's a monster.