Well, I'm no expert, but I can suggest a few-
A Glock 19 in 9mm, Glock 23 in 40cal, or a Glock 30 in 45 ACP are all similarly sized and priced. Their polymer frames make them exceptionally light, they're utterly reliable, very durable, simple to operate, and the tenifer finish makes them very corrosion resistance. High-capacity mags can be had for the 19 & 23, holding 15+1 of 9mm and 13+1 of 40cal rounds respectively, and the 30 holds 10+1 of .45 in its stock mags. I carry a Glock 19 in the spring and fall, when jackets and windbreakers make concealing a pistol easier. Seeing as you are a lot bigger than me (an earth-shaking 5'5, 140lbs), you'll probably find it a whole lot easier to conceal any one of these three pistols. Expect to pay around 450-550$ new for anything in the Glock line, but used pistols can often be had for less. In fact, you can buy a factory refurbished Glock 19 or 23 with 2 hi-cap mags out of the Gun List for 450$. Used and refurbished Glocks are usually a good buy, because they're pretty much indestructible anyway. Those would be my first choices in a full size pistol. They're the best combination or concealability, firepower and light weight.
If you're looking for something a little smaller, a Glock 26 in 9mm or a Glock 27 in 40cal is a good choice. They're a good bit smaller than the first three, with all the good points I first named. They hold 10+1 of 9mm or 9+1 of 40cal, respectively. With these two I'd recommend a Pearce grip extension for your pinky, because a full grip makes these little numbers a whole lot easier to control. I find the 40cal to be a handful! They're around the same price as the first three.
Another great buy in this size is the Kel-Tec P-11 in 9mm, or the P-40 in 40cal. They're slightly smaller and lighter than the mini-Glocks, same capacity in both calibers, and about half the price (A buddy of mine just recently picked up a brand new P-11 for 233$, tax and all). Reliability is very good (although I wouldn't compare it to a Glock out of the box); with a little "fluff and buff" internet magic it's excellent. It's only down point is the L-O-O-O-N-G trigger pull which takes some getting used to, but with a little practice it becomes second nature. I hate to admit it, but the little P-11, in my hands, is as acuurate as my bigger Glock at 25 yds once I got used to the trigger. Buffing the trigger assembly a-la the internet makes it MUCH easier to shoot. Check out the Kel-Tec Owners Group for more info on this pistol. Again, I'd reccomend a grip extension for either model. When my Glock 19 is indiscreet for carry, the Kel-Tec P-11 rides easily in a jacket pocket or on a belt clip under a sweatshirt.
My last choice is going to draw some fire - but I like it. Kel-Tec also makes a 32cal pistol, the P-32, which is probably the most concealable pistol I've ever seen. It weighs less than 10 ounces fully loaded with 7+1 rounds of 32cal, and is VERY thin. Reliability is very good, and the price is about 200-240$. Sure, the 32cal isn't the last word in a defensive round, but it's miles better than nothing, and this little pistol will go anywhere you can put a pocketknife or wallet. I'm really going to like it come summertime when the 90 degree+ days will make a t-shirt and shorts standard attire. It's really hard to conceal a pistol with minimal clothing, but the P-32 will make it world easier.
I hope all my long-winded advice helps. good luck!
------------------
"Oh yeah? Well I talk LOOOUDLY! And I carry a BIIIGGER stick! And I'll use it, too." -Yoesemite Sam
