Yes, there are several ways to get the Death Attack ability without being evil.
- The Avenger PrC is basically a good-aligned Assassin, including Death Attack. It was published as an April Fools article, so may not count as "official content" for some DMs, but it was published by WotC, and it's no more ridiculous than the Slayer of Domiel (BoED), which is also a good-aligned Assassin (though it gets Death Touch rather than Death Attack).
- A high-level Binder (ToM) can bind Marchosias to get the Death Attack ability.
- The Black Dog PrC (Dragonmarked) gets Death Attack as a class feature.
- The Dark Hunter PrC (CW) gets Death Attack as a class feature.
- Cultist of the Shattered Peak (LEoF) gets Death Attack as a class feature.
- Telflammar Shadowlord (Unapproachable East) gets Death Attack as a class feature.
- Justice of Weald and Woe (CoR) gets Death Attack as a class feature.
- Imaskari Vengeance Seeker (Underdark) gets Death Attack as a class feature.
- Marralurk (Sandstorm) gets Death Attack as a racial feature.
None of these options require the character to be evil-aligned.
However, it should be noted that Death Attack is, in many ways, even more limited than Sneak Attack:
- You make the Death Attack only as part of a Sneak Attack, which means any opponent who's immune to your Sneak Attack (Plants, Oozes, Elementals, Undead, high-level characters with Improved Uncanny Dodge, anyone wearing Heavy Fortification armor, etc.) is also immune to your Death Attack.
- You have to study your target for 3 rounds before using Death Attack. That means, at best, you're getting off one at the beginning of a fight, then relying on regular Sneak Attacks after that. And that's only when you're getting the drop on your target.
- It's Fort negates, and it's hard to get the save high enough that important targets will reliably fail, even if they're theoretically vulnerable to the attack. (As KRyan points out in the comments, this can be somewhat dealt with by taking multiple classes that provide Death Attack, many of which will stack with each other for purposes of calculating the save DC.)
This info was pulled from this list. I found it by Googling 3.5 "lists of stuff" "death attack" (expecting to find my answer in this excellent collection), but found the linked page instead, which was just as good. Next time you have a "what are all the ways to [do X] in D&D" type of question, try something like this - you might be able to answer your own question!