Using a rooted cm9 htc sensation and so far it's been good for me. Pretty good screen if not looking at it from the side, which is silly to me why reviewers talk about looking at the screen from an angle... But that's just me. With cm9 it's not as heavy as sense ui.
Samsung galaxy s II is very speedy but phone might be kind of huge. Still a great phone imho, probably won't be 300 though.
On the cheaper side my father in law has an lg mytouch which is pretty solid. Not sure what to comment about it except it's close to a budget phone these days.
Gsm nexus s is another good option. Super amoled screen is vibrant. Stock Android and easy to customize.
The Samsung blaze is nice too. Little brother to the SGSII. But not android 4.
For Web surfing dual core phones help with simultaneous page rendering and java script processing. Something with Android 4 and chrome beta will be nice for browsing. Unless your wife needs flash.
Good luck!
On a side note... If your wife will just use it for wifi and can put it in a purse... The new nexus 7" tablet might be a consideration, should be only 200 on the google play store in July hopefully... Thinking of getting one myself!
Sent from my HTC Sensation using Android Central Forums