I've been away from Oblivion for quite a while now, just got the urge to reinstall everything and play again. I got a bunch of mods installed without too much issue (FCOM, texture replacers, OBGE, etc), but I am having trouble finding suggestions for ini edits. I've searched UESP and different wikis and came up with some decent performance tweaks, but I haven't seen anything relating to lighting or HDR or anything like that. Any suggestions?

For the most part, it is recommended to leave the Oblivion.ini alone. Some things can be tweaked; download Wrye Bash (or you should have it being your running FCOM), there are some tweaks included.

Yes, nowadays my .ini is nearly 'factory default.' I enable screenshots and disable dialog zoom and borders and that's about it.

Really? That's very strange to hear... I recall doing so much to that poor beast back in the day XD So does everyone use default lighting and HDR settings, or is there another utility or mod for those? The lighting just feels kinda flat with the current settings...

There is a school pf thought that performance wise the stock .ini is pretty good. However, if you are using large texture replacers increasing uInterior Cell Buffer,
uExterior Cell Buffer, and iPreloadSizeLimit, I have found, helps.

And I agree about stock HDR settings. I use:

Yes I use default. I do however use the Oblivion Script Extender and Graphics Extender to add fancier features. Day's are bright, nights are dark, dungeons are dimly lit, basically the best lighting you can get without adding dynamic shadows which Oblivion doesn't support.

What values would you suggest? I'm using 4GBs of RAM if it matters. I ask because I remember seeing value suggestions in the past, but don't know if these are still considered optimal. I'd try out your HDR tweaks too, but I'm not sure how they'd look with All Natural and OBGE's Godrays. ^_^

To the OP, I personally haven't tweaked much this time around other than disabling borders, lowering the density of grass rendered, increasing grass diversity (for Diverse Grasses), and lowering uGridDistantCount and uGridDistantTreeRange. I'm sure I also did a few other minor things I've forgotten.

Here's a list of all setting changes I've made.

I personally tweak things in my Oblivion.ini file due to certain mods I'm running, e.g. RAEVWD actually suggests making some changes depending on how many VWD objects you're loading. I combine these with fog management mods to make my distant landscape look a bit more realistic (in my opinion).

Set bBorderRegionsEnabled=0.Set bUse Joystick=0.Set bAllowScriptedAutosave=0.Set bSaveOnTravel=0Set bSaveOnWait=0Set bSaveOnRest=0Set bSaveOnInteriorExteriorSwitch=0Set iMinGrassSize=80Set fBrightScale=1.7500Set fBlurRadius=6.0000Set iShadowMapResolution=1024Set bUseWaterReflectionsMisc=1Set bUseWaterReflectionsStatics=1Set bUseWaterReflectionsTrees=1Set bUseWaterReflectionsActors=1Set bLocalMapShader=0Set uGridDistantTreeRange=14 (Note: 15 is default)Set uGridDistantCount=14 (Note: 25 is default)Set fLightLOD2=4500.0000 (Note: 1500 is default)Set fLightLOD1=4000.0000 (Note 1000 is default)

What settings you pick for some of these things will depend on your system. I have a high-end system and graphics card, and lots of memory, but I'm also running a lot of memory-intensive things so it's always a balancing act.