Fighter/Cleric type was always one of my favorites.
Rogue/Swordsage is great, especially with feat Rogue if doing Rogue 4 / Swordsage x. For mainly Rogue, Swordsage at ECL 9-10 to get Assassin's Stance, Island of Blades stance, Distracting Ember and Cloak of Deception manuevers works well for sneak attacking. Plus, then at level 9 you can grab Shadow Blade and add dex to melee damage.
Monk 1 (or 2) / Druid x is nice, though if the DM lets you get wis to AC from a monk's belt, fairly pointless.
Before all the splat books, especially Tome of Battle, came out, getting a level of Barbarian was nice for my Rogues. I liked being able to search for traps and still have speed 20, so it didn't slow the party down. The d12 HD and +1 BAB helped in combat, and Rage 1/day was a nice panic button to have. With all of the splat books, I created a 2/3 feat Rogue with the rest as levels in Barb (by level 16 it would have evened out to an 8/8 split) who was loads of fun, using Whirling Frenzy, Wolf Totem (tripping and scent), Lion Totem (pounce), and eventually some other Barb variant to use Str for Intimidate checks along with the Rogue side giving UMD and tons of combat feats to have a very fun "battle artist." He could trip, use Knockback to hit AND bull rush people, then using domino rush to play a game of bowling....very versatile character in and out of fights. Felt like I was using a martial adept without actually having martial maneuvers.
I always liked the idea of a Hexblade/Monk/Kensai build focused on defense and counterattacks that was just frustratingly hard to hurt -- Evasion and Mettle, Arcane Toughness, Withstand to auto-pass Reflex saves, high AC with Expertise feats, Defensive Throw and Hold the Line to counter anyone who either a) charged at him, b) missed attacking him, or c) both. Oh, and Deflect Arrows from Monk to stop ranged attacks, too. Of course, that idea was back from when C.Warrior was the only complete book out. Nowadays, I'd want to add in Tome of Battle goodies, like the Counter Charge maneuver (and other Setting Sun stuff), Evasive Reflexes feat to backpedal out of reach as foes provoke AoOs, etc... With the Diamond Mind save replacers, Kensai might not be needed for the build anymore.