which software you choose depends on what your needs are. are you opening an ebay store, if so is it consignment, business liquidation, or hobby based? if you aren't planning on doing a high volume of sales, ebay has their own free software. you plan on running a business, you will want something that is 3rd party. check out the reviews under the software and services tab.
Some of the software listed in that category hasn't been updated for a while and may feel outdated (even though it should still work fine). The more up to date programs include eBaitor, AlienFiles, and Trendy Listing Builder.
If you want more features, such as posting to eBay as well as generating the HTML, starter programs you could consider include eBay's own Turbo Lister, SpoonFeeder, and Auctiva (web-based).
If you try any of those a review would be much appreciated!