I'll second the 550D. Fantastic bit of kit.
The other alternative is the sony NEX range... from £130 used. As well as the sony lenses, you can adapt a fantastic array of incredible older glass as well, the caveat being you need to be able to manually focus. The NEX has aids to do help this though. I'll be getting one next payday.
Same applies to the Canon DSLR bodies, I'm using Contax, Yashica, Leica, Pentax, Olympus OM, Exakta, Rollei and M42 lenses with appropriate adapters on my 20D - of course you have to reckon in the so-called crop factor that extends the focal length equivalent of the legacy lenses you use - 1.6x Canon and 1.5x NEX.
In other words, your standard 50mm lens is equivalent to an 80mm on a Canon and a 75mm on a NEX.
That's something that can get really critical the smaller the sensor is due to the effects of camera shake at what are then very long focal lengths.
To be honest, manual focusing in low light is a bit of a bu..er with the dim pentamirror viewfinders of Canon DSLRs (you only get a pentaprism viewfinder in the top models), although a model with live-view helps a lot.
Canon DSLRs also have an automatic, aperture and focal length-dependent exposure compensation for Canon AF lenses that can't be switched off and leads to slightly wrong exposures at smaller apertures when using lenses attached with adapters.
The top of the line models have an option for dialing in the initial aperture that lets you get around this.
Canon DSLRs are also not particularly weatherproof - as a tense 2 hours with a hairdryer on low after a short shower proved in the case of my 20D - thankfully it still worked after treatment.
Cheers