There are several options to try:
Do it yourself with one of these packages, free or cheaper than a specialist recovery service http://www.ptdd.com/ BUT if you are at all unsure about this, go to a data recovery service as DIY might make it worse as @Sirex points out.
A specialist recovery service. I have used these myself with success. These folks were great: http://www.rapid-data.net/ (if you are UK-based). They recovered 2 external drives for me, one ordinary and the other a truecrypted volume (I supplied them with the correct password obviously). I don't work for them by the way. Very reasonable prices but made more expensive by their forensic partner having to recover the truecrypt (with the correct password I gave them).
If you don't live in UK just search for data recovery in your favourite search engine. That's exactly how I found these guys.
OK it was an expense for me to recover but I sure feel good getting my data back! I'm philosophical about it and liken it to an expense on repairing my house or car. If you can afford it, do it. Accidents happen.
I hope it works out for you.
It's no good anyone saying should have backed up in first place, hindsight wonderful thing that didn't help me before I got my data recovered and one kicks themselves when they think of that. However, having been bitten, I'm quicker to back things up more regularly, on different media: DVD, Blu-ray, and a Lacie RAID NAS. For the DVD/Blu-ray backups, I also keep a simple catalogue database , a big HTML table actually edited in OpenOffice Write. This is backed up too and so I know where to find my data.