To be honest it depends on your app, to use a siemens + ethernet card might be a bit expensive, however there are a number of HMI manufaturers out there that have web enabled hardware.
Beijers is a good one, they are reasonably priced & ones above the E300 range support an optional ethernet card (about £170) that will give you what you want, also they will talk direct to Mitsi & AB plcs + most others, also you can use passthrough mode to talk to the plc with you programming software so if the HMI is connected to the only port on your PLC you can still program PLC via the HMI.
I believe that Proface is another one.