For an activity that Americans spent $30 billion on this year, buying a new television offers lousy choices. Cathode-ray tubes look sharp but are too big and boxy. LCDs are kind of fuzzy and hard to see from an angle, and run the risk of dead pixels. Plasma screens are too pricey and heavy. That's why the market is wide-open for the arrival of SED TV in July. SED, or surface-conduction electron-emitter display - a technology developed jointly by Toshiba and Canon - combines the sharpness of a CRT (by firing electrons at a screen) with the slim form of an LCD or plasma. The Japanese companies have been working on SED TVs for a while, garnering plenty of buzz with prototypes at trade shows and waiting until the price came down enough for mass production. Early SEDs are expected to cost $10,000.