Halfling monk! Yes,  yes, a thousand times yes!  I've been playing one for about six months now (just hit level 11), and it's been an absolute blast.  He makes a great sneaky character.  Here's my advice (sorry if some of this sounds like power gaming):
- 20 Dex, and get a magic item to boost Dex further.  My character's got 23 dex, and he's one sneaky mofo.
- Flurry of Blows is your friend, as is Stunning Attack.  One problem many players have with the monk is that they don't use the special abilities enough/correctly.
- If you can, get into the Shadowdancer prestige class (from the DMG) sometime after level 10.  You want 10 levels of Monk, because at 10th level you get Ki Strike +1, which is helpful for overcoming DR.  The Shadowdancer class gives you lots of nifty abilities to enhance stealth, like hiding in plain sight.
- If you have a mage in your party, try to take advantage of Bull's Strength, Cat's Grace, and the Wisdom improving spell (sorry can't remember its name... Owl's Wisdom?).  They're all a huge help.
- Another thing I just thought of, and I could kick myself for not thinking about this sooner, is that you could take Weapon Finesse (Unarmed) if you decide to go high dex.
- If you can somehow get your hands on a Robe of Blending, that's great fun for sneaking (+15 to Hide!).  Plus, the Robe's "change self at will" ability comes in handy if you're in a stealth situation where you're *going* to be caught.  Suddenly, you look like a lost little child! 
Roleplaying a halfling monk can be something of a challenge.  I tend to think of halflings as free-spirited and mischievous, which runs a bit counter to the disciplined nature and lawful alignment of monks.  The way I explained it was this:  Cade (my character) is an orphan who was raised by the clergy of Yondalla.  When it became obvious that he wasn't cut out to be a cleric, they trained him as a monk, which they saw as the "next best thing".
One thing too about my halfling monk: due to all the crazy AC bonuses you can rack up, he has a 24 AC with no armor on.  +1 for being small, +2 for his Monk bonus, +4 wisdom, +6 Dex, and +1 for a special (non-magical) item that all the members of party have one of.
I kind of stumbled onto the idea of a halfling monk because I wanted to play stealthy, but Rogues have never really interested me all that much.  Anyway, go for it and have fun. 
