Check out
Strap Freak for leather straps.
They are out of Indonesia, I've ordered from them several times (including some custom sizes) and they've always delivered as promised.
Holbens also has a nice selection of straps and bands (and they ship super fast), but I've found that in general Strap Freak leather is higher quality.
Hirsch has some cool straps as well, their high end stuff is decent quality but their cheap straps tend to break down quickly.
For a decent steel band at a fair price I like the Oyster bracelets from
Miltat.
I have one of their Super Oyster
316L 22mm straight link diver "B" bands on my Tudor Heritage Ranger.
Of course it's not Tudor quality, but it's also $70 versus $800 for a Tudor factory stainless band and it punches well above it's price.
Here's a Pulchers 23mm strap from Strap Freak on my Zenith bronze, it took about a month to arrive. Not bad for a semi-custom strap (23mm isn't a size they normally offer).