Please pick a DSLR for me

Pentax K-R ( 18-55mm )
Nikon d3100 (18-55mm)
Sony a33. (18-55mm)
Sony nex 5 (18-55)

See your question in photography

Between the two dSLRs you listed, I pick the K-r!

Sony a33 and Sony nex 5 are NOT dSLR's. A33 is an SLT (Single Lens Translucent) and NEX-5 is a mirror-less camera. A33 is alright, and at least looks like a dSLR, and supports minolta lenses etc. But NEX-5 comes with poor quality lenses, and actually looks ugly with any lens other than the 16mm prime.

Between Pentax k-r and Nikon d-3100 it's a tough call, they are both good in their own ways, but I will choose Nikon d3100.
But if Pentax k-r is cheaper than Nikon d3100 (which I expect it to be), then go for Pentax k-r, it will save you some money, and to be honest it's not much different from Nikon or Canon entry level dSLR's.

Pentax K-r and Nikon D3100.It depends on which feature you prefer. Those Sony's aren't real DSLRs.

Here's a DSLR Buying guide - http://www.the-dslr-photographer.com/2009/11/which-dslr-to-buy/