Both of those lenses are good, low-cost "training wheels" companions to the EF-S 18-55, and are, in fact, the lenses I got when I bought my Canon XT/350D back in 2006, but today, there are two choices that might be better.
EF 50mm f/1.8 II pros and cons
This is an amazing bargain and is easily the best value-for-price lens Canon makes, but that's partly because its pricetag is so very very low. It is an all-plastic lens, with a plastic mount bayonet, a fiddly manual focus ring, no distance scale, and iffy autofocus performance in low light. And the main reason you want it is the f/1.8 max. aperture. Compared to the 18-55 @55mm, the difference between a max. aperture of f/1.8 and f/5.6 is that you can get 3.3 stops, or 10x the amount of light from that aperture setting. That means to get the same exposure, you could use an iso setting that's 1/10th of what you'd have to use with the 18-55 kit, or a shutter speed that's 10x faster.
However, the EF 50/1.8 II is a film-era design from 1990. In 2012, Canon came out with a new lens, the EF 40mm f/2.8 STM. It's slower than the 50/1.8. But sharper at f/2.8 than the 50/1.8 is at f/2.8, it's a little wider, so it's closer to "normal" field-of-view on a crop body camera, and it's a pancake lens with a metal mount bayonet, so you're liable to still use it as a travel lens or as a lens cap you can shoot with, if you move on to a more expensive and faster prime as your "permanent" lens. It's also only about $50 more than the 50/1.8 II.
EF-S 55-250 IS
The EF 75-300 III is a very low cost lens. Its design goes back to the '80s. You can get nice sharp images out of it, but it's more limited than other lenses in that capability. You have to stop it down past f/8 for better performance. You have to keep the shutter speed above 1/300s (or higher) to mitigate camera shake blur when shooting @300mm. It's a little softer at the extreme ends of the zoom range. A lot of lenses have similar issues, but the usability of this lens can be limited.
For about $100 more, the EF-S 55-250 IS is a digital-era design, and is stabilized. Its performance wide open at 250mm is better than the 75-300 @300mm wide open, and can even rival the 70-300 IS USM (non-L)'s. The only ways in which the 75-300III beats this lens is on price, and if you also have to use the lens on a full-frame/film camera.