Not used a VA, sorry.

I've used iWriter for articles - be very specific about what you want. The basic level writers usually need a bit of editing but their quality seems to improve as the article gets longer (because they only get paid if you approve).

Transcription: Fiverr. A couple of years back it cost me $5 per 15 minutes.

Some graphics: Fiverr but it can be hit & miss so I also use Freelancer. Again, be specific. For instance I'll spell out that 3 different designs doesn't mean the same design in 3 different colours. I've had most success on graphics on Freelander with Eastern Europeans.

Simple bug fixes on websites: Fiverr. Including fixing scripts, scary htaccess stuff and more.

Programming can be hit and miss on Freelancer and you have to know what you're talking about otherwise they can try to pull the wool over your eyes. Same goes for website design.

I had a database tuned up on Freelancer and the guy was really good (a Russian living in New Zealand).

PeoplePerHour I've recently had some success with on a website redesign. As with Freelancer, take the time to read the reviews (not just the star ratings) and talk with two or three that you shortlist before awarding the project.