There's at least three dozen Oly/Zuiko, Leica and Sigma lens options available in the 4/3 mount system. Also, with an adapter, you can manually use lenses from other manufacturers such as the Nikon F' and Pentax K's.
Although, as pointed out, the sensor is smaller in the Evolt series, there comes two possible advantages which are worth considering, in my opinion. One is that the 4/3 system sensor will have a greater depth of field, which is helpful when shooting landscapes. The second advantage, and the greater one to me, is that the 4/3 ratio is closer in dimension to standard print sizes. This has allowed me to not worry so much about having to overcompensate when framing a shot for cropping later on when I make prints, thus not wasting as many pixels. However, to be fair and as already pointed out, there is a price to pay for the smaller sensor in regards to noise and resolution.
I own the Oly Evolt E-500 and I will tell you straight up, I do not regret it for one minute. I just loved the way it felt when I first picked it up. My only big beef with it has been the size of the viewfinder, which is way too small. None the less, I have come to adapt. Plus, IIRC, the 510 was the first or second DSLR to have live preview which means you don't have to always have your eye in the viewfinder.
By kit lens standards, the two that come in the Evolt series kits are head and shoulders above Canon's standard kit lens and cover almost all my needs in normal lighting conditions. However, still being low end lenses, they are not going to perform as well in low lighting situations; sometimes having another stop or two would be nice. But in the case of the Evolt series, I do agree that you get more bang for your buck with the kit purchase.
So, with all that being said, probably the biggest factor is what kind of budget you are working with. If you're like me and don't have a lot of money laying around or if you're relatively new to using SLR/DSLR's and want to get some seat time without worrying about having to invest a lot of money for a year or two, then I'd go ahead and go with the E-510. If you're already seasoned and are ready to lay down the dollars for additional lenses right now, then I might consider other options. Personally, I'm not an "Oly" person or a "Canon" person. I work with what's available within my resources and the Evolt E-500 (which I've had 2 years now) fit the bill perfectly. Later on, when more resources are available, I'll have the luxury of not being as frugal.
Also check out
http://www.dpreview.com/reviews/OlympusE510/ for a great review of this camera.
