I've soloed Kara, Gruuls, Mag, TK with my Hunter with an item level of about 470 at the time. Tonight I did 10 man Sartharion w/ 3 Drakes up, took me a a while to figure it out but I finally did it. And I did it as a Marksman hunter spec'ed hunter. My current iLevel is 480. I still have a couple blue items.
My first TK run and KT kill about 2 weeks ago, and KT dropped Ashes of Al'ar.
I am not a good player, and I can solo all the LK raids. Though, I struggled with Naxx 20 with the end boss until I googled what I needed to do. I don't know if I could solo Naxx 25, but I plan to try this week.
Vanilla through most of Wrath is soloable by every class. Most of cata is soloable by Hunters/DK's/Paladins at the very least and I'm sure there's a few others.
All BC instances are soloable
All of them. However you can still wipe on some if you dont know the fight mechanics.
As a DK, I can say that every raid in BC is soloable:
Magtheridon - go balls to the wall to burn down the adds. When they're all dead, face roll the boss.
Gruul's Lair - For council, kill the healer, then the one who fears. After that, it's smooth sailing. Gruul is a joke.
Karazahn - Chess is your only challenge. Watch vids and make sure that your king always has a vertical and horizontal space open for when Medhiv cheats.
Tempest Keep - All fights are easy except Kael'Thas. Make sure to kill each adviser in a different corner. Put the warrior in the top left side, the mage in the bottom right, paladin goes in top right, and engineer goes in bottom left. Kill the mage first, then pally (AMS to counter fear), then unload on engineer. Warrior is a joke. Burn KT afterwards, but watch your healing.
SSC - whole place is a joke. Make sure to kill adds on Hydross. For Vashj, go blood spec. She'll get a lot of stacks, so it's nice to pocket heal yourself while you wait for toxic to spawn.
Hyjal - Lich boss - watch out for his AoE, it's bigger than the graphic. Other bosses are cake.
BT - Watch Najentus for spike to pop his bubble. Clear Akama's room before pulling, pop army for P2 of Reliquary, and kill the chick during council fight. Spit on Illidan when he doesn't drop the warglaves.
Sunwell - Burn the Frostwyrm before she MCs you, and I like to kill Fire Sister first because she does a conflag. Oh, and make sure to kill the SLAYER during trash since they do % damage which can wipe you.
Did I skip one?
What I wrote assumes you understand how the fights work normally.
Some might be slightly tricky with low gear but otherwise there's not much challenge.
Kara: Easy (Only chess event may take some time)
SSC: Easy only Vashj can be tricky
TK: Easy (If u for some reason have trouble on Kael'thas, try spreading the adds)
Thanks to rivellana for this awesome signature.
The only person I have any issue with is Vashj in SSC. The chess game in Kara used to frustrate me until someone showed me a guide somewhere that illustrated just how easy it can be.
Notable fights, Brutallus in SWP is going to be hard without some defensive cooldowns, a large self-heal, or decent DPS (My Ret pally is woefully bad.)
Chess event is a bit RNG. There's pretty reliable strats on the web, so do some homework.
TK is a joke now, Kael's four adds have about ~2-300k health each, meaning they'll go down in 1-2 shots from a 550+ geared toon.
Hyjal was pretty easy. Notable fights is the pitlord(I can't remember his name) who casts doom on you. Your pally can bubble out of it, but your DK and Warrior will need to kill him before it goes off. ~1.5 mins.
Vashj has been nerfed (somewhat) recently. You can move while holding the cores. It's not really a tank&spank fight, so you might want a jist of what to do before going for it.
Soloed on a 525 ret pally all raid in bc are soloable
You could solo all but ssc during cataclysm.
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