What standard UART rates are there?
It started a long long time ago with teletypes — I think 75 baud. Then it's been mostly doubling ever since, with a  few fractional (x1.5) multiples, for example 28,800, where there were constraints on phone-line modem tech that didn't quite allow it to double.

Standard crystal values came from these early baudrates, and their availability dictates future rates. E.g.,

\$\begin{align}{7.3728 \,\mathrm{MHz} \over 16} &amp;= 460,800 \;\text{baud}\\\\{7.3728 \,\mathrm{MHz} \over 64} &amp;= 115,200 \,\text{baud}.\end{align}\$

Most UARTS use a clock of \$2^n \times 16\$ of the baudrate,  more modern parts (e.g. NXP LPC) have fractional dividers to get a wider range by using non-binary multiples.

Other common standards are 31,250 (MIDI) and 250K (DMX), both likely chosen as nice multiples of 'round' clocks like 1MHz etc.