I was thinking about getting a sig soon. What is the difference between the p228 and p229? It seems like the 229 can accept 9mm, .40 or .357 while the 228 is 9mm only. The website specs seem to show only a 20 mil length difference and 2 ounce weight difference. So what is the point of the 228? The 229 seems like it is better in every way from just these facts.

Also, what is the deal with the sig pros? What do they have to offer over the other sigs?

The 228's were designed just for 9mm. The 229 came afterwards when people were looking for the same size pistol in .357 and .40. They are practically the same except for the caliber and the side serrations on the 229 only go halfway up.

The Sig Pros are nice, they are Sigs only Polymer framed pistol. I just picked up an SP2009, it's lightweight and very accurate. They are substantially cheaper than the classic sigs because of the polymer frame. The only downside about it is the dissassembly.They are a PITA to field strip/assemble.

The 229 was designed for the full power .40 round .
They use a milled slide where the 228's were stamped steel .

I remember reading that the 229 frame was beefed up
in some areas , but in a side by side I never could see
a difference .

Quoted: The 229 was designed for the full power .40 round . They use a milled slide where the 228's were stamped steel . I remember reading that the 229 frame was beefed up in some areas , but in a side by side I never could see a difference .

The 228 also uses a separate breechblock installed in the slide.  The 229 slide is one-piece.

229>228

Quoted: The Sig Pros are nice, they are Sigs only Polymer framed pistol. I just picked up an SP2009, it's lightweight and very accurate. They are substantially cheaper than the classic sigs because of the polymer frame. The only downside about it is the dissassembly.They are a PITA to field strip/assemble.

compared to the metal SIGs yes but on their own it's really not that bad.
Not like field stripping a Ruger mkII

P229 on the left, P228 on the right.

size wise they are nearly identical.  If you want a 9mm, get the P228, as it is slightly lighter and the slide isn't quite as blocky.  If you want a 40 or 357, get the P229.  

ETA, the frames of the P229 9mm and the P228 are the same, they use the same mags, and a slide from a 228 will fit on a 229.  The 40/357s have different mag wells.  

The P229 is heavier but not better IMO. I like both for the differences. I had the P229R first then bought the P228. They shoot smooth and accurate.  The P228 is easier to carry and feels lighter plus it's a stamped steel frame versus the P229R's forged steel frame. I am glad I got both.