[RPG] ny way to sneak attack oozes

What you are talking about is combat facing variant, which indeed allows to turn your back to the fighter and not fear the sneak attack from the rogue. There is no such option in the standard rules.

Otherwise, seek cover (tower shield, preferrably animated), concealment (if Tome of Battle is mundane enough for you), uncanny dodge or any protection from critical hits (not that it can be obtained in mundane ways, though).

The primary tactic

...to avoid being forced to flank with sneak attack is to cause them to otherwise lose their Dex to AC, which also allows sneak attack.

Being blinded, stunned, in a grapple, or flat-footed (surprised, climbing, balancing, surprise round of combat if you win initiative, etc) all normally cause one to lose the Dexterity bonus to AC (but watch out for special feats or class features that may override this).

Skills

Hiding is your friend:

If you’re successfully hidden with respect to another creature, that creature is flat-footed with respect to you. That creature treats you as if you were invisible.

Note also the sniping entry in the Hide skill (see Rules Compendium for the latest updated text on Hide). Flat-footed = able to sneak attack. So long as you can stay hidden, you can sneak attack all day long. See also Total Concealment and Total Cover. Note that Total Concealment often cancels the need for a Hide check, a sneaky way to make that Hide check with the hefty penalty from sniping. DM call, though. Abuse it at your own risk.

Using Hide can make your opponent flat-footed, but you still have the immunity issue to address...

Powers and Spells

Improved invisibility or Invisibility will deny your opponents their Dex, unless they have a see invisible effect of some kind.

The lowly Grease spell forces a balance check upon anyone in the area of effect when they try to move, which oddly means that they are now automatically flat-footed, even if you succeed the check. Ergo, automatically vulnerable to sneak attack. Note that if they stay put, they only have to make a Reflex save and are not flat-footed. Also, if they have 5 or more ranks in Balance, they are not considered flat-footed when attempting to balance. If they fall, they are prone, but they are still not flat-footed, though they will provoke an AoO if they try to get up.

Grave Strike, Golem Strike, and Vine Strike spells allow you deal sneak attack damage for the duration of the spell as if the creature (undead, construct, and plant respectively) was not immune.

Blink also works, though most people prefer items with the blink effect.

Psionics are generally great for sneak attacking, as you can use the Sneak Attacking with Spells rules for the attack, and use your Psicraft skill to suppress the power display, which effectively makes most powers non-obvious. Combine with Hide for a truly sickening sniper type. Note that a lot of attack powers have secondary displays which cannot be suppressed like the primary display, so that hide check can become critical. Most of the non-obvious ones are [Mind-Affecting], which has it's own issues as to what it can and can't attack, so be aware.

Feats

Razing Strike feat allows you to sacrifice a spell, do bonus damage based on the spell level and get extra damage equal to your sneak attack damage. Note however that this is not a sneak attack itself, even though it benefits you by your having sneak attack.

Supernatural Strike feat allows you to deal critical damage to creatures normally immune to crits (undead, oozes, and constructs are listed as examples) if you roll a threat against the creature, and then confirm the threat. (Note, that this feat is from the d20 Modern SRD, and is thus compatible with 3.5, which is part of d20. But check with your DM first.)

Items

The weapon crystals of truedeath and demolition allow one to sneak attack undead and constructs respectively.

Items with the blink effect are popular, as are the various 'strike' spells mentioned above.

Deathstrike Bracers - sneak attack elementals and oozes.

Dagger of Deadly Precision +4d6 damage*

Rogue's Vest +1d6 damage*

*Bonus damage when making a sneak attack, this is not an increase to actual sneak attack dice of damage.

Class Abilities

SkullClan hunter Divine Strike - seems to deal bonus damage equal to sneak attack bonus damage when attacking undead.

You already know about penetrating strike. I seem to recall a ranged attack option ACF that allowed one to ranged flank in one of the combat oriented complete books. Ranger oriented? Causes them to count as flanked until your next turn, iirc. Helpful for setups, anyway.

There is a psionic class that allows one to flank from non-standard positions. Complete psionic - Elocater. Again, helpful for setups.

Conclusion

There may be more, this is just off the top of my head. I did not cover all the methods to boost sneak attack damage per se, but a few appear in my list.