Jessops 360 AF seems to get plenty of attention at £70 and it does TTL. Some of the Yongnuo ones are good value, athough not rock-soild (that can be aid about most sub-£100 flashguns). There are quite a few YN ones that do TTL but many have been designed as off-camera units so only fire in manual mode. Sigma also does some useful guns but they are above £100. Sunpak is a good name also. Nissin is supposed to be brilliant, although I know jack about them
If I were you I'd look at the used market and buy the best you can afford. A cheap, not-so-good flashgun will do most things but when it comes to things like FP sync, CLS, rear curtain sync and just general use, you'll always find that the Nikon flashes rule the roost, although more and more optios are available these days from other nbrands. If I were you I'd look out for an SB-600 or an SB-28DX, something digital compatible with a whole host of features, easy controls and decent power. You can still get older Nikon SBs like the SB-24 that will work on your camera, but you won't have full TTL, just manual mode and A, which is an auto mode that's linked to aperture settings I think. Ffordes have one in for £39 - they're rock-solid and will probably outlive you
EDIT: found a few used for you...
http://www.mpbphotographic.co.uk/us...ns/jessops-360afd-flashgun---canon-dedicated/
http://www.mpbphotographic.co.uk/us...uns/metz-48-af-1-digital-flashgun--for-nikon/
http://www.mpbphotographic.co.uk/us...edicated-flashguns/nikon-sb-600-speedlight-1/
http://www.ffordes.com/category/Fla...rtDirection=Ascending&SortExpression=ItemName
Used dealers like
MPB, ApertureUK, Ffordes, Mifsuds, Carmarthen Cameras are all reputable - I've used all of them and have never had a problem with any used items I've bought from them. They all rate their gear truthfully and in some cases, the product has actually been in better condition than was stated.
You can still pick up some bargains on fleabay but you A) have to win the auction (not always easy with flashguns), and B) hope that the product is as-described and fully working. I've bought a few older Speedlights off the 'bay and they've been fine but they've always been back-up guns and mot ones I'd stake my life on to performs perfectly until the end of time
