would love to get some shout outs for first road bikes for a new triathlete... did my first one on a mountain bike and i did okay but definately want to get a road bike for more races ;)
I did my first tri on a rigid mountain bike with a set of slicks on it, so I understand where you're coming from. I've been a mountain biker my whole life and when I got into triathlons, I quickly realized I needed to get a road bike. I purchased a Trek 2.1 with Shimano 105 components in 2010 and have been very happy with it. I didn't want a specialty TT/Triathlon bike because I wanted to use it for racing, as well normal road riding (and I didn't have the budget for both). I also looked at the Specialized Allez. Hope this helps. I've competed in 4 triathlons.
I can't help but second the comment from ssaba... If you want to do triathlons but also plan to ride 'for fun' or just around town I would get a road bike. They are much more comfortable and universal than a triathlon focused bike.
Finally, your actual question, I don't have a personal preference for manufacturer but I recommend trying to get into a "105" level component group. It is a step up from the Sora / Tiagra components and I really think it is worth the slight cost increase.
If you are on a tighter budget try to find a used bike on craigslist or buy a clearance "last year's model" in the fall or early spring. Of course you also need to make sure whatever you buy fits you properly.
I think I approached this issue from the opposite end of the spectrum, as someone who had never really done any riding but was looking for a bike that would work well for recreational riding as well as in the occasional tri.
I went with a Trek 1.1 as an entry level bike and recently upgraded to a 2.1. I've found both to be incredibly durable and functional for hard rides/races as well as more relaxed touring type rides.