i am buying some dlc for obolvion and i was wondering which one i should buy what do u think r the best one beside shevring isle i already got it

Knights of the Nine, All plug ins that benefit your character(s)... For example if you have a Mage, Assassin and a thief, you should get Frostcrag Spire, The Vile Lair and Dunbarrow Cove, respectively.

Any, except Orrery and Horse Armor, really.
KotN is the best of them all IMO.

I just started KOtN a few weeks ago and so far it seems to be the most interesting DLC.

I liked Shivering Isles as well, but there was something about the art direction that felt like a different game.

thanks do u know if GOFTY edtin comes with all of these or what

Yeah, pretty sure it comes with all of them except the Fighters Stronghold.

GOTY on CD only comes with Oblivion, SI and KOTN as far as I know: http://www.uesp.net/wiki/File:Oblivion_GOTY_Boxcover.jpg
I understand from UESP that GOTY steam includes them all?

More detail on the DLCs here: http://www.uesp.net/wiki/Oblivion:Official_Plug-ins

My very subjective take (your mileage may vary):

Battlehorn - don't have it.
Wizard's Tower - nice if you like crafting magic and don't want to be in the guild of mages.
Thieves Den - I like it alot. You get to be like mayor of your own little pirate cave.
Vile Lair - Not my cup of tea - too dark and assassiny for me. Don't care for http://i668.photobucket.com/albums/vv43/Acadian6/buffy1.jpg.
Horse armor - Love horses, but have not interest in armoring them.
Orrery - A simple quest, but I like it very much because the reward special powers all add the 'drain attribute' abiltiy to your spell book. One of the few ways to get that ability for non PC players.
Mehrunes Razor - Very nice giant dungeon crawl. The namesake weapon makes an ok cheese knife to display on a table.
Spell tomes - I don't bother. I suppose if you are not on PC and really want to summon a black bear, it might be worth considering.
KOTN - Large and enjoyable if your character has any streak of nobleness or heroism in them. The Relics are quite interesting.

Also worth mentioning, Mehrunes Razor has the best "Stealth/Assassin/Thief" armor in the game. The Morag Tong Armor.

I have them all, and am generally unimpressed with most. I have not tried the Orrey and Thieves Den yet though. To be honest, you can usually find better from mods, which also have the bonus of being free.

In my very jaded and completely personal opinion:
Battlehorn Castle - Big house that is way out of the way near the edge of the map. A fight with some marauders to get it, and some undead in the basemant. Eh.
Wizard's Tower - Another house that is out in the middle of nowhere. Has the bonuses of spellmaking and enchantment altars. But since I am on the PC, I have no need of either. Also has teleport pads to all mages guild houses. But I can fast travel if I do not want to go through the trouble of walking to another city.
Thieves Den - Has a pirate ship as I understand, so that is a plus. Possibly interesting if you are a thief.
Vile Lair - A handy lair for vile people that is off in the middle of nowhere. Lots of ambiance. Has an easy victim for vampires, if you are too lazy to sneak up on a beggar sleeping in an alley.
Horse Armor - Makes horses look prettier if you take the Elven Armor. I never use horses because you cannot fight on them, and picking alchemy from their back is awkward.
Orrery - Have not tried it yet. But I understand that the reward is a power that changes depending on the time of the month (the alignment of the stars and all that). As they are all once a day powers, I would never use them anyway. I never use powers like that.
Mehrunes Razor - A very fun dungeon crawl, with a very cool ruin in the later part. The uniform the bad guys wear seems a bit silly and is just a retextured tunic from the original game. It seems they could have just did a retext on a briastplate for the same effort, and have it look like they are wearing armor instead (which imho is more believable attire for an army bent on conquest). The reward itself I found to be useless. But getting there was fun.
Spell tomes - You get to have a Breton conjurer attacking you over and over. Plus some books with spells that you could just make yourself if you really wanted them.
KOTN - Has a fun quest to perform (although not quite a good as the Mehrunes Razor one), and a suit of neat mail armor that looks like it is straight out of the IRL Crusades. Has the bonus that the armor upgrades itself as you level, something Bethesda should have included with all the quest award items in the vanilla game. A good dlc for a sword and board religious good guy character. Plus the boots keep forest animals from attacking you (but you can just download the mod in my sig for that).

Forgive me for one tiny correction to your very astute observations:

Quote UESP: 'Once you have all the pieces, return to the University and talk to Bothiel, who should be waiting in the Arch-Mage's Lobby (you do not need to be a member of the Mages Guild to complete the quest)'.

Indeed, anyone can enter the basic lobby of the Arcane University and talk with Bothiel.

Reference link: http://www.uesp.net/wiki/Oblivion:Repairing_the_Orrery

Ahh yes, sometimes I forget that.