The Nasdaq index made record highs last week, approaching the 5,000 level and breaking through the "dot-com bubble" highs of the year 2000. This could understandably generate some concerns among investors, and it's generally a good idea to be cautious when the markets are trading at record levels. However, make no mistake, none of this means that all tech companies are necessarily overvalued. Far from that, dynamic growth leaders such as Apple (AAPL 0.59%), Google (GOOG 1.37%), and Priceline (BKNG 2.16%) are still trading at attractive valuations. Here's why:

Apple
Apple is clearly booming: both the stock and the underlying business. The company delivered a spectacular earnings report for the December quarter on the back of massive iPhone sales. Apple crushed Wall Street forecasts with a 30% increase in sales and a jaw-dropping jump in earnings per share of 48%.

Adding to the excitement, Apple will be bringing its new Apple Watch to the market in April, and there are strong reasons to believe the company is exploring the possibility of building its own electric vehicle in the coming years.

Source: Apple

With this in mind, it's no wonder why Apple stock has risen by almost 70% in the last year. But this does not mean that Apple is excessively valued; on the contrary, the company trades at a discount versus the overall market. Apple stock carries a forward P/E ratio near 14 times earnings forecasts for the coming year, considerably lower than the average forward P/E ratio of 18.5 for companies in the S&P 500 index.

Investors seem to be concerned about slowing growth in the future, which could clearly be a possibility as the smartphone market matures over time. However, iPhone unit sales grew by an impressive 97% year over year in BRIC countries during the last quarter, so there seems to be considerable room for expansion in high growth emerging markets.

Not only that, but Apple is allocating tons of capital to share buybacks, which reduces the amount of shares outstanding and increases earnings per share. Apple reduced its diluted share count by 7% during the year ending in December 2014. In addition, new products such as Apple Watch and Apple Pay could provide additional growth venues in the years ahead.

Google
Google (GOOG 1.37%) (GOOGL 1.46%) is not a very popular pick nowadays. Google stock is down by nearly 5% over the last year, missing the Nasdaq rally as investors seem to be much more inclined toward social media companies such as Facebook (META 2.91%), which is rapidly gaining market share in online advertising, delivering an explosive increase in sales of 58% during 2014.

Source: Motley Fool

Google is not growing as rapidly as Facebook; as sales grew 19% in 2014. However, the comparison is not entirely fair, since Google is a much bigger company than Facebook: The online search giant produced over $66 billion in total sales during 2014, that's more than five times Facebook's revenues of $12.5 billion during the year.

It's only natural to assume that Facebook and other dynamic players in social media will gain some ground in online advertising in the years ahead. However, the industry should provide more than enough room for multiple companies to grow and even thrive over the long term.

After all, Google is still the undisputed king in search, the company owns more than 75% of the U.S. search market according to StatCounter, and it enjoys a privileged position in mobile thanks to the enormous popularity of its Android operating system. Google owns many of the most valuable online properties in the planet, including Gmail, Chrome, YouTube, and Google Maps, among several others.

Google is trading at a forward P/E ratio of 17.7, which sounds like a very reasonable valuation for such a dominant online juggernaut.

Priceline
Priceline is the undisputed global leader in online travel services, an industry in which it has produced extraordinary performance over the years. Priceline has delivered an annual average increase in sales of 29% per year through the last five years, and profit margins are stratospherically high, above 36% at the operating level during 2014.

The company has a big presence in the European hotel market; this is a crucial strategic advantage from a competitive point of view. However, a depreciating euro is dragging on performance over the last several quarters. In addition, Priceline is aggressively increasing its investments in marketing and advertising, and this could generate pressure on profit margins over the coming quarters.

Source: Priceline

In this context, Priceline stock has fallen by more than 10% in the last year, and it's now trading at a forward P/E ratio of 18 times earnings estimates for the year ahead, in line with the S&P 500. 

Nevertheless, even while facing challenging conditions, Priceline keeps delivering outstanding financial performance. Total gross travel bookings purchased by customers were $10.7 billion during the last quarter, an increase of 17% year over year and growing 23% on a local currency basis. Revenues grew 19.4% versus the same quarter in the prior year, to $1.84 billion.  In spite of all the difficulties, Priceline delivered a 23% increase in adjusted EBITDA and a 22% jump in earnings per share during the quarter. 

If this is what Priceline is delivering while facing challenging conditions, just imagine what it can do when conditions turn for the better.