InGale - Thank you for the comments...hopefully we can help you get the right camera for you...there are lots of great ones out there, so by no means do my answers to your questions mean that I think this one is the only one that would be good for you...I just wanted to directly answer your questions, as well as add a little information to correct some comments that have been made that are a bit incorrect, at least with this camera.
I saw that you took your photos with various lenses. Do you have some photos made with the kit lens?
I don't, unfortunately - I bought my A550 as a body-only camera, forgoing the kit lens since I already had the 18-250mm Sony zoom lens purchased with my A300 previously. The quality of the 18-250mm lens is about the same as the kit lens, with the difference being that the 18-250mm has significantly more reach at the long end. From 18-70mm they would be about the same speed and optical quality.
Can I mount a philter on A550 kit lens?
Absolutely...the kit lens comes with normal threading on the end to attach filters as needed.
How often do you recharge the battery?
Not often at all - the battery life on this camera is extremely good - it is CIPA rated at nearly 1,000 shots - and that's with viewing, flash use, etc. In normal daytime shooting, I'll typically charge my camera once every 3 weeks, running off around 3,500-4,000 shots a charge. One definite perk of the Sony cameras using this battery is the Infolithium system which gives you an accurate battery percentage remaining meter, rather than a little 4-bar graph...so you can reliably run the battery down to 10% or 5% in the field without worrying about the camera dying any moment. I charged my camera last week on Oct 1, shot with it on Oct 2 &3, then again yesterday and today, for a total of around 1,800 shots total, and as of now, it's still reading 41% remaining.
Is it compatible with battery grip?
It is. Sony makes a battery grip for the A500 & A550, which is capable of taking two FM50 batteries.
I understand that A550's body made of plastic and not metal; is it really important?
Well, it isn't to me - what's most important to me is build quality and ergonomics. I've got no problems with the build - as the camera is solid and meaty, and can take some bumps - I've shot very heavily with mine for a year now, in tough conditions and it still looks and feels like new. It does have a metal chassis, as do almost all DSLRs...it just uses more extensive plastics on the body. I don't know that I'd drop it from 6 feet onto a rock - but I would try not to do that even with a full mag camera!
Just a quick comment on EvanK and jwnrw's comments re: live view - they are right as it applies to every DSLR made by all manufacturers...except Sony. Sony's live view system is entirely unique and those who have never used it or seen it don't know its abilities...so they might not realize that Sony's live view system doesn't have the same compromises that the other systems do. First of all - paired with the tilting LCD, it does make it a viable alternate to using viewfinders, for example, using it with waist-level medium-format style shooting, candid shooting, tripod mounted shooting, etc. And it is also good for when you need to get at funny angles or shoot from ground level, where you may not want to lay down on the ground to get the shot. Secondly, Sony's live view system continues to use the phase detect focus system, same as when using the optical finder. It focuses identically fast as when in OVF mode - with no focus performance degredation at all. The switch between optical and live view is 100% seamless and identical in usage. Third, there is no shutter delay or half-press delay when using live view to shoot. Other live view systems must perform a series of mirror maneuvers and focus maneuvers before taking the shot, where you can press the shutter and wait as long as 1 second to get the shot. The Sony live view system has no shutter delay, shooting instantly at shutter press, and capable of even firing bursts at 4 frames per second. It is entirely unique in the DSLR world. Fourth, the A550 uses a dual live view system - it offers the quick live view mode mentioned above, and it also offers a second system which works like that of the other DSLRs...it is slower, and uses the main sensor to provide the view - the reason one might occasionally use this mode is for accurate manual focusing or framing a shot in extremely low light, as it can be zoomed in as much as 14x for accurate fine focusing, and can gain up the view significantly allowing you to see a scene well enough to focus and frame when the viewfinder would otherwise be of no help.
That said - I must confess - I am an eyeglass wearer, and I use the viewfinder probably 80% to 85% of the time I shoot. Most DSLR users do use the viewfinder...it does allow for better stance and stability, and makes it easier to track and pan with moving subjects. Still, I specifically went the route I did because I wanted a camera with Sony's live view option - it comes in handy enough to make it high on my list of must-haves - for odd and low angle stuff when shooting wildlife, and for tripod and night shooting when I use the live view exclusively working off a tripod.
And by the way...OP means 'original poster'...usually used to refer back to the person who posted the original thread!
As many have mentioned, and it can't be mentioned enough - ergonomics is a biggie - handle the cameras if you can and make sure the ones you are considering feel good in your hands. And feel free to ask any other questions you may have!
Sony DSLR-A580 / Sony 18-250mm / Minolta 50mm F1.7 / Sigma 30mm F1.4 / Tamron 10-24mm / Tamron 200-500mm / Tamron 90mm F2.8 macro / Minolta 300mm F4 APO
Sony NEX5N / 18-55mm F3.5-5.6 / 55-210mm F4-6.3 / Pentax K adapter / Konica K/AR adapter / bunches o' Konica & Pentax lenses!