Gah! Holy geez! Ok this is in-game, people! Stop acting like he has to use the standard uber-crazy set.
Here's what will make a solid in-game moveset:
Surf- An absolute must. Suicune is a water type. Surf is the best water-type move. The end.
Ice Move- It needs some kind of Ice move. Ice Beam is the best, yes. But Blizzard could work well too, it's easier to find. The only time you'll need to use this move is when Grass types threaten you. In all fairness, Suicune shouldnt even be fighting a grass type. If it is, you're better off having the Mondo-super-powered Blizzard behind you to take it out in one hit.
This is totally incorrect. Suicune not only uses Ice Beam against Grass-types, but mostly against Dragon-types that resist its Water move. An Ice Beam boosted from a Calm Mind also hits types that are normally neutral to it pretty hard too. Suicune, with proper EVs and Calm Mind and Rest, can battle against Grass-types all day long without needing the inaccurate Blizzard.
Dig- Actually works. Before all of you hardcore Gameboy/Pokebattle competitors chew me out, hear what i have to say. This is in-game. Dig offers a good way to counter electric types. With prediction, dig can evade the impending Electric attack and score a REALLY good hit on the electric type. This isn't competetive battling. The AI in the game is stupid. No one switches on Dig/Fly in the game. Dig is a fairly solid choice.
Time for some chewing out. LOL I blame these bad perceptions on the programmers of the game that make novice trainers think everything is about "Super Effective" moves. Dig is a HORRIBLE move on Suicune. It doesn't matter that it is "Super Effective" against Ground-types. What they don't understand is that an unboosted STAB Surf that feeds off of Suicune's higher base SAtk (90 compared to 75 base Atk) does almost the same damage of an unboosted SE Dig. It is almost identical. The big difference is that while Dig takes two turns to inflict that damage, you can do the same damage in one turn with Surf. You can also use one turn to Calm Mind and increase both Suicune's SAtk and SDef, which not only makes Surf hit harder (making it a 2HKO against Jolteon instead of a 3HKO), but it allows Suicune to take less damage from a STAB Thunderbolt that is also SE. So, as you can see, Dig is absolutely useless on Suicune, especially if you are smart and use Calm Mind.
Calm Mind- Its merits have already been discussed.
Roar- Is always fun. Sometimes, there's just a good situation to use Roar.
Protect- Always a viable choice, but I don't really reccomend it too highly here.
Toxic- Same as protect, it can have a use on any Pokemon. Makes a great filler move.