We analyse the large-scale correlation function of the 6dF Galaxy Survey (6dFGS) and detect a baryon acoustic oscillation (BAO) signal at 105h-1Mpc. The 6dFGS BAO detection allows us to constrain the distance-redshift relation at zeff= 0.106. We achieve a distance measure of DV(zeff) = 457 ± 27Mpc and a measurement of the distance ratio, rs(zd)/DV(zeff) = 0.336 ± 0.015 (4.5 per cent precision), where rs(zd) is the sound horizon at the drag epoch zd. The low-effective redshift of 6dFGS makes it a competitive and independent alternative to Cepheids and low-z supernovae in constraining the Hubble constant. We find a Hubble constant of H0= 67 ± 3.2kms-1Mpc-1 (4.8 percent precision) that depends only on the Wilkinson Microwave Anisotropy Probe-7 (WMAP-7) calibration of the sound horizon and on the galaxy clustering in 6dFGS. Compared to earlier BAO studies at higher redshift, our analysis is less dependent on other cosmological parameters. The sensitivity to H0 can be used to break the degeneracy between the dark energy equation of state parameter w and H0 in the cosmic microwave background data. We determine that w=-0.97 ± 0.13, using only WMAP-7 and BAO data from both 6dFGS and Percival et al. (2010). We also discuss predictions for the large-scale correlation function of two future wide-angle surveys: the Wide field ASKAP L-band Legacy All-sky Blind surveY (WALLABY) blind Hi survey (with the Australian Square Kilometre Array Pathfinder, ASKAP) and the proposed Transforming Astronomical Imaging surveys through Polychromatic Analysis of Nebulae (TAIPAN) all-southern-sky optical galaxy survey with the UK Schmidt Telescope. We find that both surveys are very likely to yield detections of the BAO peak, making WALLABY the first radio galaxy survey to do so. We also predict that TAIPAN has the potential to constrain the Hubble constant with 3 per cent precision.