I've been having this weird issue where Oblivion now always crashes within a few seconds of loading a saved game, no matter if it's an autosave, streamline save or a normal save. This isn't a matter of it being a new game either, my character's clocked 50 hours.

Here's my mod list:

If you go back several saves, 5 or 10 maybe, does it work?

Yeah, but that doesn't explain why later saves are unplayable when nothing's changed in the load order.

I had that issue today. Try loading Oblivion without OBSE (through the normal launcher) and see how it goes.

Edit: I did that, saved in a new slot and in a new location. Loading that solved the problem for me.

Are all the crashes at the same location? If so, then it is probably not so much an issue with the save but with the location.

One possible problem is a corrupt spawn. Something is trying to spawn and it is crashing your game. Sometimes, you can back up to a save before you hit that location, and that save will work. What you'll want to do is go indoors, wait out the respawn time (72 in-game hours by default) and then try entering the area again. If the spawn point spawned a different something this time, you might not crash.

Well, I tried saves at Cheydinhal, Hoarfrost Castle and the DB sanctuary. Same issue.

Here is general list of solutions for that problem in the past. You will have to see which applies to you.

Problem
My game CTDs when I try to load a save game.
Cause
Various reasons, such as a 'missing master', load order, or mod conflict.
Solution (things to try)
Option 1. Rebuild your '\My Documents\My Games\Oblvion\Oblivion.ini' file, by renaming the current one, and starting the game with 'Oblivion_launcher.exe'. At the first menu, select 'Options' so the game re-detects your hardware, set any settings your need here, and exit. (Do NOT attempt to play from this point.) Re-install any HUD or User Interface mods, or restore mod related settings from the previous version of the INI file. Resort your Load Order with BOSS, rebuild your Wrye Bash 'Bashed Patch' if you use one, and try again.
Option 2. Check for and remove any OBSE Plugins that are no longer used.
Option 3. Test remove any mods known to cause problems in some instances.
Keychain v5.0 [http://oblivion.nexusmods.com/mods/3409%5D

Problem
In some areas the game crashes within seconds of entering the area.
Cause 1
Requirement for specular lighting in the areas, while it has been switched off.
Solution
Set Specular Distance in the in-game video options to minimum.
Workaround
Set the variable bDoSpecularPass in Oblivion.ini to 1 if you switched it off before. You can turn it back off after you're past the problem area.

Cause 2
Corrupted master file. Casual crashes in Oblivion are to be expected, but sometimes the crash corrupts the master file causing exceptional crashiness in damaged areas (and as result likehood for further corruption of the file).
Workaround
Be in the first person perspective mode. As soon as you enter the area, look straight down at the floor and run to the desired exit door using your feel (map, hints from the floor looks), without looking up. Of course you can't do much in such areas that way. It can get you, say, across the Skingrad castle courtyard though.
Solution
Reinstall Oblivion. Your saves shouldn't be lost but just in case back them up (My Documents\My Games\Oblivion\Saves) then uninstall Oblivion (with Add/Remove Programs), reboot, install Oblivion again, possibly reboot again. Most likely your savegames are still present, if not, recover from backup. Don't start with a savegame created in the crashy area, pick an earlier one if needed. If you would prefer not to reinstall the game, you can restore your autosave. Go to your Saves directory (commonly C:\Documents and Settings\"user name"\My Documents\My Games\Oblivion\Saves) and delete autosave.ess. Then rename autosave.bak to autosave.ess. Occasionally, the .ess and .bak will not have been generated during the same save, so restoring the .bak will result in starting from 2nd most recent autosave point. For reasons unclear, following the steps in Solution 2 will cease corruption of autosave files also.
Solution 2
Stop overwriting existing save files and avoid using Quicksave. Disabling quicksaves will have a dramatic effect in reducing crashes. Supporting the hypothesis that corrupted saves cause game crashes rather than game crashes corrupt saves, it seems that clicking "new save" everytime will eliminate those pesky "crash on area transition" crashes. Autosave is still ok.

Cause 3
iShadowMapResolution was changed from 1024 to 256 in Oblivion.ini for patch 1.2
Solution
Open Oblivion.ini. Find iShadowMapResolution. Change 256 to 1024. Close Oblivion.ini and save changes.

Cause 4
HDR lighting is enabled
Solution
Just go into video settings and turn HDR lighting off.

Cause 5
Internal shadows are turned off. Sometimes going through a door will immediately CTD.
Solution
Turn on Internal shadows.

If none of those help, try to be a little more specific about the circumstances of the crash, especially with regard to repeatability. Can you trigger the crash at will? Is it always at the same place (and where is that: exterior or interior, etc.), how much RAM do you have and have you checked to see if you are hitting a memory cap (around 2GB if you don't have the LAA patch)? That sort of thing.

-Dubious-