Mexico would be my destination of choice probably but that obviously is not what you're asking
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Lake Fork in Texas is an excellent choice. It's only a short drive (4-5 hours or so) from me in Oklahoma. I've only been there twice but the bass fishing was excellent both times.
We caught a ton of big bass on the first two day trip. We fished mostly 10 inch plastic worms. I think the biggest bass I caught was around 8 pounds. We caught several bass over 4 or 5 pounds, and I don't think we caught but one or two bass smaller than 2 pounds. In total we caught about 35 bass on the first trip.
The second time we didn't fare quite as well, but the weather was horrendous and we had to get off the lake on the second day it was so bad. We still caught several big fish in the 6 to 8 pound range though.
Both times we fished Lake Fork in the dog days of summer.
I just love Lake Fork. It's just kinda got that air about it. It may be because it was in its heyday when I was a young kid dreaming about catching that HUGE bass over 10 pounds. Lake Fork was almost unreal to me as a young teenager. The possibility of catching a bass over 15 pounds on every cast, fishing plastic worms in those trees...
That first trip, I guess we were 18. We pulled up and some guy was walking up the boat ramp with a 9 pound bass he had just caught fishing from the bank! What an awesome fishing trip that was!