The Sonic Blaster
The Sonic Blaster, more commonly referred to under it's more high tech name of 'The Squareness Gun' first made it's appearance as a weapon of Captain Jack Harkness in The Empty Child/The Doctor Dances. The blaster used a sonic wave projected into the form of pulsing squares of blue light which could cut through thick walls, and also had a reverse function which could replace the removed chunk of material afterwards. This was a flaw as well as a help though because doing so usually meant that it would completely drain the batteries, rendering it useless. After leaving the blaster behind in the TARDIS, it managed to find it's way into the hands of River Song, who brought it with her on her expedition to the Library during series 4, where it helped the team to escape from the Vashta Nerada.
The Species Matcher
It has only made the one appearance so far, but the brilliance of The Species Matcher means it is more than worthy of a mention here. It fell into the hands of the Doctor as a gift from his Godmother, though he never used it until he was in his eleventh incarnation. The Species Matcher is capable of identifying the species of an individual by their image, and though it takes it a while to work properly, it get's there in the end. Much like the Doctor on occasion. This though was less practical than most other gadgets and had to be worn in harness straps on the upper body, and as evidenced in Vincent and the Doctor, this can be quite an inconvenience if you are trying to identify a monster that is chasing you down the street. We last saw it with it's mirror shattered by the krafayis, but here's hoping that it get's another outing sometime soon.
The Vortex Manipulator
Rarely used by the Doctor, who saw it as more of a 'space hopper' compared to his 'sport's car' of a TARDIS, the Vortex Manipulator has nonetheless remained a favourite with Captain Jack and River Song, being used on multiple occasions to get them, and even the Doctor at times, where they need to be in a hurry. It didn't just whizz you through time though, oh no. With a flick of a switch there can be Princess Leia style hologram messages being sent to anyone with compatible wristwear. Add to that the fact that it can be used for tracking multiple life forms and even taking control of other bits of technology and we have quite a nifty little gadget. It would also appear to be virtually indestructable too, surviving a bomb blast that left its wearer literally in pieces. And I bet it even tells the time, too.
The Sonic Screwdriver
Oh come on, don't say you didn't see it coming. The Sonic Screwdriver has got the Doctor out of more scrapes than we even care to try counting, we couldn't leave it off this list now, could we? Ok, so it has perhaps become a little overused of late, and yes, perhaps the list of it's uses has become ridiculously long, but where would we honestly be without it? If it hadn't have unlocked those taxi doors in The Runaway Bride then Donna would have ended up having to pay the full fare! And what about that Champaigne bottle in Voyage of the Damned, eh? How else would they have got the cork out? If it wasn't for those pesky deadlock seals that turn up randomly out of nowere in the strangest of places, then there wouldn't be a single thing the Sonic Screwdriver couldn't do. Of course, the Screwdriver has it's more important uses too though like disabling teleports and bringing down perception filters and has been helping the Doctor since his Second incarnation, so despite its more recent overuse and it's seemingly endless 'get out of jail' uses, the Sonic Screwdriver is well deserving of it's place at the top of any tech list.