I am in possession of a one year multiple entry type B visa and my 90 days will come up soon.

From Bangkok where is the least hassle location to do a quick(couple of hours total time) stamp in and out? Is it Poi Phet Cambodia?

I have to go to the states next month and don't really fancy Singapore or KL just for a new entry stamp which I will use for a few days only.

Any suggestions?

Most in and outs take less than a hour,depending on line ups. Pick the closest border or look at going by plane to Penang or Vientienne which may be faster than going by bus to the border.

I did Bkk\Aranyaprathet by train 47Baht (6hours) tuk tuk to Cambodian border 50Baht (10mins). Cambodian Visa 1000Baht, Oiled 2 greasy palms 100Baht each for forms and "helping" with the Visa, and a further 100Baht "fine" because I wanted to do an immediate turn around and not visit Poipet - paid to Cambodian Immigration for exit stamp.(20mins). Tuk tuk Back to Aranyaprathet in time for Air-con Govt bus back to Bkk 164Baht (4 1/2 hours). Time at border 20mins. Total time spent 11hours. Use the bus both ways and it will cut this by 90mins. I went mid week, leaving at 6am. Stress-free, interesting scenery. Hope this helps.

Is leaving a bit earlier for the US an option ? Seems a less onerous thing rather than a hassle for a few days only ?