I suggest you to buy Sony brand. Because Sony is the most powerful brand for camera. They make good pixel camera.
Got a good chuckle.
After that highly detailed and specific product testimonial, I certainly am convinced! I shall be dumping all my other gear forthwith! I just hope I can recover a little bit of money from it -- now that the word is out that it's not very powerful.
On a more serious note... a DSLR is a bit of a departure from a point & shoot. The camera body will not guarantee better results. It's just a better tool which will make it easier to get better results IF you learn to use the tool. In other words: A DSLR is not necessarily the best camera for everyone. If your needs are simple, you may be happier with a point & shoot or... even an advanced point & shoot or "bridge" camera. Every camera will do well when there's plenty of light for an easy exposure. A DSLR offers more control over the visual appearance of the resulting images. It is, for example, MUCH easier to create a tack-sharp subject while having a deliberately out-of-focus background using a DSLR and the right lens. This is something that is extremely difficult if not impossible to do with a point & shoot. But it also assumes the person taking the photo wants that level of creative control. A DSLR tends to be more responsive... focusing and shooting substantially faster than a point & shoot (even considerably faster than a very high end point & shoot.)
Also keep in mind the potential costs involved with a DSLR. Most will include a "kit" lens. That is almost always a lens with standard working zoom with a moderate wide angle to a relatively moderate telephoto... nothing extreme. If you're looking for something with 10x or 20x zoom... this is not that lens. But the quality of the lenses tends to greatly exceed those of point & shoots and since the lens is removable, you can attach a lens which is ideal for your shooting needs of the moment. So the camera you get when you buy it is really just the beginning of what's possible... you can expand the "system" by buying additional lenses and other accessories. On a point & shoot, the lenses are not removable. The camera you get is all that it will ever be -- there is no expansion. But these better lens options come with a price tag... the least expensive DSLR lens would probably cost about $125 ... and go up SUBSTANTIALLY from there (there are single lenses that cost in excess of $10k -- there are even lenses that have sold for over $100k. But these are not lenses us mere mortals use. The lenses us mortals use may cost $300, $500, or $1000. Some fairly high-end lenses can cost as much as $2000-2500 for JUST the lens.
Another possibility with a DSLR is your lighting options. This is part of camera ownership that misses a lot of people entirely. Lighting can make a HUGE difference and a big impact, but to have the impact you need to be able to get the light off the camera. This is more than most people want to do. But whereas a external flash hot-shoe and the ability to use off-camera lighting is a standard feature on most any DSLR, extremely few point & shoots have this as an option (on the highest end point & shoot cameras can do this.)
I tend to nudge people towards either Nikon or Canon equally (I shoot Canon, but frankly both companies make extremely good products.) This is mostly because if you are buying a DSLR camera and you suspect you may enjoy it, you may find yourself buying more gear. Canon and Nikon enjoy the widest selection of OEM gear choices as well as the largest support from 3rd party vendors. If you need an accessory and you own a Canon or a Nikon... odds are if the thing exists at all then it'll be available for a Canon or a Nikon. It *might* be available for Sony, Olympus, Pentax, etc... but support for those brands trails far behind.
You mentioned the Sony a350 and the Canon XSi, but you didn't mention which Nikon (DSLR is just a generic label for "digital single lens reflex" camera and applies to any camera with a reflex mirror and removable lenses.)
The Canon XSi is no longer marketed. It's been (long) since replaced by the T1i (which was replaced by the T2i, T3i, T4, and now T5i.) The T3i, T4i, and T5i are still currently marketed (the T5i was only very recently announced and available). The T3 (without the "i" suffix) is Canon's lowest end DSLR which is still currently marketed. Canon's entry level bodies get an "i" suffix if they were at the high end of the entry-level range when they were released. The Rebel bodies which do not have an "i" suffix are targeted at the low end of the entry-range.
For Nikon, the entry range includes all cameras with 4 digit numbers starting with either 3 or 5. E.g. D3000, D3100, D3200... or D5000, D5100, or D5200. The D3000 and D5000 are no longer marketed. The D3200 is the latest of the low-end entry range (the D3100 was it's predecessor although it is still marketed and sold). The D5200 is the latest of the high-end of the entry range (and similarly the D5100 was it's predecessor).
These are all extremely good cameras. A "poor" DSLR is still generally more versatile than a "good" point & shoot ... so it's hard to make a "wrong" choice.