The Black and Decker GH900 Trimmer is a wonderful choice if you are on a budget but still want something that does an almost flawless job and has a lot of power. For small to moderate yards this thing will eat up weeds like they weren't there.
The Hitachi CG23ECPSL is a wonderful gas powered trimmer at a really good price. What sets it apart from most other weed eaters is it is a delight to use - so comfortable and it packs a lot of power. Plus you get a fantastic seven year warranty!
The Black and Decker LSTE523 has possibly the best line feed on the market, a good amount of power and is really comfortable to use. The battery and charger aren't great, but as long as you don't have a huge yard this will be easily good enough for you. Read my full review.
The Toro Corded String Trimmer 51480 has a huge amount of power is really well made and doubles up as a fantastic edger. Just a shame it is let down slightly by the auto-feed system. Read my full review for a warts and all opinion.