The economy may croak from the credit crunch, but public offerings and acquisition deals are happening at the fastest pace in years. The fourth quarter is going to be monster.

Some 46 U.S. companies backed by venture capitalist registered during the third quarter to go public, according to research by Dow Jones VentureOne to be released tomorrow. Not all of them will go public within the next three months, but even if half of them do, that’s way more than in any quarter in recent memory.

If you VCs have been bullish already, these returns on their investments will make them even happier.

See the full report here (downloads Excel, a large file with several tabs) Note that only venture-backed companies are covered here in the research, which means some companies aren’t included. Since the Internet bubble burst, the most IPOs in a single quarter was 24, and that came in this year’s second quarter. Any more than that during the next three months, and the fourth quarter will be the biggest since the boom year of 2000.

Separately, the Dow Jones report shows that 90 venture-backed companies raised more than $10.5 billion in merger and acquisition transactions in the third quarter, a 31 percent increase over the same period last year and the highest quarterly amount since 2000.So far this year, $28.4 billion has been raised via M&A transactions and another $4.7 billion raised in public offerings, all but guaranteeing that this year will be the largest year in the U.S. for venture-backed liquidity —both in terms of IPOs and M&As— since the dot-com boom, said Jessica Canning, Director of Global Research for Dow Jones VentureOne. “Yes, after several years of uncertainty, the ‘venture capital rebound’ is officially over.”

Another interpretation: Maybe its the credit crunch that has everyone in a fluster. Do the deal now, or else….

It was a relatively sleep summer of IPOs, with only 11 companies going public. Still, even that was more active than last year’s nine IPOs.

More biopharmaceutical and medical device companies have filed to go public (22) than information technology companies (18). The number of clean-tech company IPOs in registration (two) looks quite anemic. Internet-Web 2.0 companies aren’t represented among the IPO candidates either.

Another factoid: The largest acquisition — the $812 million purchase of interactive advertising firm Right Media by Yahoo —was more than all the capital raised via IPO during the third quarter. The largest IPO of the quarter belonged to medical software company Athenahealth, which raised $90 million.

The report also shows that the time between initial venture investment and M&A-IPO also reached its highest level ever in the third quarter at seven years for M&As, and 8.5 years for IPOs.