New bike for beginner

I know that you are looking for a new bike, but I would suggest that you also consider that the biggest bang for your $800 is going to be a good 2-3 year-used bike - Tri or road.  Are there any Tri teams in your area, especially women-only teams?  If you get to know some of the other local members, you will find that there is often a network that knows who is selling what bike and if the bike was well maintained.

Try to find a LBS where you feel like you honestly trust that they are giving you sound advice on the best bike for you vs. just 'selling' you a bike.  Ask lots of questions.  It's great to develop a relationship with your LBS.  I've been to a few shops within an hour of here and my loyalty is to one and one only.  I love the guys at this one local shop (always so helpful), and have just not had the same experience elsewhere.

 As someone else mentioned, don't forget all the little stuff on top of the base price of the bike.  It adds up fast and was not something I had anticipated.  To give you an idea...helmet (yeah, I didn't even think of that), shoes, peddles, water bottle cages, water bottles, saddle bag with the appropriate stuff in it to change a flat, 1 pair of decent bike shorts, lube for the chain.

 My bike is a Specialized Dolce Elite, a fairly baseline road bike, and while I have nothing to compare it to, I have been very happy.  I was planning to spend closer to what you are thinking and ended up going one step up.  With that said I have owned it for 6 months and am wishing I had a tri bike.  I just hated to spend the money for a tri bike when I had no idea if I was going to even like triathlons.

When I bought my very basic, entry level road bike 4 years ago I wasn't sure I'd even like cycling so I didn't want to spend much money. The entry-levels are usually in the $600-$800 range, but I got mine for a little less by buying the previous season's model. They had one that was an ok size for me so I took it. It's been a good bike to get started on and I've done all of my training, some centuries and now my tris on it and just now upgraded to a tri bike.

But I agree with the previous post about used bikes. If you can get your LBS to size you for a bike, you can look for a nice used one, which should allow you to get something a bit better for a lower cost. I'm assuming you have some equipment already since you're competing in tris so you may just need to add clipless pedals (highly recommend them) and shoes on top of the bike purchase.

Good luck finding the right bike! 

The majority of LBS's are currently or should be having end of year closeouts. You may be able to get more bang for your buck. One example with a tri/tt bike. Some shops are still selling the FeltS32 for $1300 plus. One of my LBS's is selling it for under $1000 out the door. If you want new, closeout time is the best. Otherwise, used is still a good choice.

edit: Stick with a brick and mortar shop. you can also contact local bike and tri-clubs for LBS recommendations. the majority of LBS will have name brand bicycles. Generally speaking the the component groups are the same on bikes within price ranges

Best of Luck

I just bought an entry-level price road bike this year and so far I am very happy with it.  It is a Trek 1.2 WSD and I got it for about $800 new.  I am a petite female (5 ft 3 in) and I didn't even have to buy the smallest size.  It is specially sized for females.  I looked into buying a used bike, but was having a hard time finding something in my size.  For me, the fit and comfort of the bike was really important.  I shopped around and tried out other new bikes in the same price range, but this one felt and rode the best to me.

Anyway, here is a link to the bike:

 http://www.trekbikes.com/women/wsd_products/bikes/2008/road/12wsd/

Just to let you know, I do some sprint triathlons and some longer rides, but I am closer in the range to a casual rider than an expert cyclist.  That said, my bike feels great after a 25 mile ride and I can *mostly* keep up with my husband and he rides a more expensive bike.