I would like to add a small update to this thread with regards to the commonly used small signal transistors, now that through hole parts are starting to vanish.
For the 2SA1015/2SC1815 and similar parts:
The KSA1015-Y and KSC1815-Y have much lower gain (typically in the 150-200 range) than the often found 2SA1015GR and 2SC1815GR. If the gain is an issue, one can use the KEC brand parts which are still available in GR rank (KTA1015-GR and KTC1815-GR), or also the nearly identical KTA1266GR and KTC3198GR.
The smaller brothers (and I believe it is the same die but in a smaller TO92s package) of the TO-92 2SA1015GR/2SC1815GR were the 2SA1048 and 2SC2458 which are equivalent to the KEC KTA1267GR and KTC3199GR still being manufactured today. The gain and pin out are the same as those for the original Toshiba parts.
For the 2SA733/2SC945 and similar parts:
Similarly, for the substitution of the NEC 2SC945 rank P or even rank K, or one can use the UTC (unisonic, Taiwan) parts 2SC945G-P which have gains typically above 350 the pin out ECB, and fit nicely in place of the extinct NEC parts or the (usually lower gain KSC945CG from Fairchild).
For the 2SA733P, KEC has made the KTA733P in the ECB pin out and with good gains (typically above 350).
For the 2SA992/2SC1845 and similar parts:
The KSA992 and KSC1845 are still being manufactured by Fairchild / ON Semi at the moment.
The 2SA970/2SC2240 are similar to the KEC parts KTA1268/KTC3200 which although are no longer made, they can still be found in ranks Y, GR and BL.
