Recently undertook a long journey that I booked through Expedia and was very happy with their service. Only needed to ring them once to tell them something, and that time their hold time was a bit on the long side (hence only 4.5 *'s) but otherwise I had no problems with them. Price was cheaper than anyone on the web for my flights - and I looked around a lot because I hate paying too much!
Booking online was easy, dozens of options offered and NO Credit card or service fee - this is almost unheard of. They emailed me with updates when flights were changed/to remind me of upcoming flights.
Overall, highly recommended.