Entei is a tough Pokémon to work with, because its Stats are messed up and it has bad moves. If your Entei has some sort of Special-based Hidden Power, I'd use it. Sunny Day is rather useless, as it gives your foe a chance to attack while setting up. Plus, Entei has a good Sp. Attack and STAB off of Flamethrowe, so you'll be damaging most things a lot without the Sunny Day. Try Calm Mind, that way you can power up not just Flamethrower and so you don't die as quickly(Entei doesn't have good Defenses). Leer accomplishes nothing, really, because it will only affect on Pokémon, and once you defeat it, then it's wasted. If you can get Substitute, I strongly suggest using it over Bite. Bite's OK, but there are other Attacks that will work a lot more.
Lonely isn't really a good Nature for Suicune, because its Attack Stat is low and you're not using a Physical Attack anyway. There's nothing you can do about it, though, so moving on:
Suicune is a lot more durable than Entei, but Rain Dance still isn't the greatest idea. Calm Mind works excellently on Suicune, because it already is difficult to defeat, and Calm Mind just makes it more so. Suicune has decent Sp. Attack, but a couple of Calm Minds will really help it out. Mirror Coat isn't all that good, because Suicune doesn't take much damage from Special Attacks, so you'll probably do more damage with Surf or Ice Beam. Rest is good for Suicune, because it can survive two turns of helplessness and it keeps it from fainting. Leftovers is the ideal Item for Suicune, because, just like the rest of its movespread, it prevents it from being defeated. Don't use a Chesto Berry, because it only works once and then disappears. Leftovers works no matter what, and that's what's so cool about them.
Raikou also needs Calm Mind(I dunno if you'll be able to get all these Calm Mind TMs, though...). Reflect is a good move, and if you can't get the recommended set for Raikou, then you should keep it. But, if you can get a third Calm Mind, then use that over Reflect. Rain Dance is the same as the first two, and if you think about it, over two turns, Thunderbolt will do more damage than Thunder will. Attacking twice with 95 power means 190 damage, whereas with Thunder you'll only get 120 because you spent the first turn with Rain Dance. Also, Thunderbolt won't miss unless your accuracy is lowered, so you don't have to Rain Dance every five turns. Spark is useless because it basically does what Thunderbolt or Thunder will, but with less damage. Substitute will help more.
I expect you won't be able to get all those Calm Minds, and probably not both of those Substitutes. Entei needs Calm Mind most, because its unboosted Special Attacks won't do a whole lot, so if you only have one, use it on Entei. If you have two, use the second on Suicune. If you don't have a third one, use Raikou's Crunch instead of Calm Mind. Raikou already has excellent Special Attack, so you'll still do a fair amount of damage without Calm Mind.
With Substitute, Entei also needs it more than Raikou. If you already have Crunch instead of Calm Mind on Raikou and can't get a second Substitute, keep Reflect. Raikou only has one weakness, so any non-Ground attack won't do much after a Reflect. Reflect also helps Entei if you're forced to switch, willingly or unwillingly. However, if you had a third Calm Mind and used it on Raikou, then use Crunch instead of Reflect, because it will help more in the long run, and you won't be as vulnerable against Ghosts and Psychics.
Overall, this is a decent team, not the best, not the worst. I'd give it a 7/10.
~*CB*~
The 8th Champion
. sorry. i meant for the second heal bell to be softboiled. i gotta check my posts more often. XD.