However, a Dwarf Assassin....
Personally I have always loved the Fighter/Thief mixture so have theory crafted a lot of different builds. There may be some improvements coming to Hide in the Shadows which would make a R21 semi-viable without HiPS, and would synergize well with a Dwarf going around in caverns and such. That said, HiPS is still the best way to be survivable as a Rogue build. Since you are going for the Fighter/Thief Dwarven Scout idea here are a couple ideas:
R21/SD3/CS6 - SD grants Darkvision which opens up Cavestalker. Ranger abilities in natural caverns/underdark environments which would fit a Dwarven Scout pretty well. No Rogue levels though so probably not what you're looking for.
R16/A8/WoD(or AK) 6 - Warrior of Darkness or Anointed Knight can support the 'fighter' side of your build and will help you get a bit higher Will Saves. Only requirement being Iron Will is made up for by free Blindfight, Toughness and Dash(WoD only, Anointed Knight gets Alertness) - all three of which can be difficult to fit in to a sneak attack build, but are all beneficial. This will get all the Rogue goodies (Epic Precision, Expose Weakness, PTWF, Epic Dodge) with Assassin Death Attack and a BAB of 24 which is a couple points higher than 'standard' rogue builds.
R16/A8/NWN3/IB3 - 14d6 sneak dice, BAB24, Feint or HiPS for sneak attacks, up to +3 AC from INT, 10% movement increase. All good stuff.
R10/A8/F12 - If you want more Fighter/less Rogue this gets you BAB25 (no 6th attack) and all the fighter feats for really high attack bonus, and damage bonus. Does not get Epic Dodge and only had 9d6 sneak dice, will have loads of feats.
R17/SD3/WoD10 - Much better saves from WoD10 and all the good rogue feats.
R12/SD4/F4/WoD10 - Similar to other heavy high BAB class builds, but by gettin 14 levels in high BAB classes and following the 'rule of 4' on Rogue and SD you end up at BAB 26 for a 6th attack (12 APR with PTWF). However, you lose way too much and it is not worth it in my opinion (Epic Dodge).
If you really do not want to get HiPS you will not be able to consistently land sneak attacks in melee, and thus you should think about other options, here are some:
Get Shield Bash, Agile Shield Fighter and Shield Slam. This allows you to build your Dwarf with ~14 DEX (Mithral Chain Mail) and max STR. You get your sneak attacks by landing Shield Slam. Works well with the builds including Fighter, WoD, and other high BAB classes that don't advance sneak dice. Idea being when you aren't landing sneak dice you are still a relatively efficient front line fighter.
Get the feat Blinding Strike. This will allow you to attempt to blind an enemy about once every 10 rounds, but read up on the mechanics to make sure your build will get a good enough DC to make it worth while.
Use a Wand or potions of Invisibility (this will get expensive!)
Build for Feint - You will be disappointed in all, but a few rare areas where it actually works decently. Most of the time it will never land. When it does it's awesome, but it's so rare as to be irrelevant.
As to your Barbarian build it is pretty tough to mess up so long as you get 20 levels of Barbarian, 21 STR And 21 CON as Aaron stated.