I'm not going to suggest a brand particularly - I find Scott MTB's fit me best, but it is personal choice. Justr try as many bikes as you can - when you find the right frame you'll know. Just try to ensure that it as upgradeable as possible so you can fit disc breaks front and back (my old hardtail can only have discs on the front).
What I would say though, is look at bikes that are a bit above your budget too - you then have to get a bit cheeky and ask for a discount and/or odd parts swapped out for the ones you want. the other year when I bought my full susser, I told the bike shop that I bought it from that I had been offered 15% at another bike shop - I didn't even need to show them the voucher (which I did have) - they matched the discount immediately.