All the king's horses and all the king's men may not be able to put Europe back together again -- but ask the market if it cares. For optimists, these rallies may seem like a dream come true. For skeptics like me, they're opportunities to see whether companies trading near 52-week highs have earned their current valuations.

Keep in mind that some companies do deserve their current valuations. Retail value store Dollar General (NYSE: DG) is one such company. Dollar General surpassed earnings estimates this week with a $0.02 beat and remains upbeat about business despite an uncertain economic environment.

Still, other companies might deserve a kick in the pants. Here's a look at three companies that could be worth selling.

Full of hot air
Someone needs to put some weights on the valuation of Nicor (NYSE: GAS) before the supplier of natural gas literally floats away. As a utility, Nicor does offer investors some semblance of stability. But the company often finds itself at the mercy of natural gas prices, the fickleness of consumer needs, and oddly, the demand for its other business subsidiary, Tropical Shipping.

In its latest quarterly filing, Nicor missed expectations by 60% as demand in its shipping business fell. What's more concerning is the lack of growth in Nicor's core natural gas business. Since 2006, Nicor's gross margin has fallen precipitously despite the company being regularly profitable. Without any real growth on the horizon and the company trading at a rich 21 times forward earnings, I'd suggest passing on Nicor here.

Try scaling this mountain
Continuing to harp on overvalued companies, I'm going to move onto Aspen Technology (Nasdaq: AZPN), a provider of software and services to the processing industry.

Aspen, despite its rapid revenue growth, has lost money in nine consecutive quarters yet bears a valuation reminiscent of a dot-com-era company. At a staggering 77 times forward earnings and 12 times book value, Aspen's valuation is considerably frothier than its closest peers Siemens (NYSE: SI) and SAP (NYSE: SAP). Perhaps the one bright spot of Aspen's recent quarter was the introduction of a $100 million share repurchase program, which could help inflate its ailing bottom-line results. But the way I look at it is that until Aspen can consistently deliver a profit, it's not worth your hard-earned money.

Madison's flagrant foul
Betting against Madison Square Garden (Nasdaq: MSG) to me seems like a no-brainer play. I mean, when was the last time the New York Knicks were relevant anyway?

OK, all jabs aside, shareholders seem to have taken the recent end to the NBA lockout with a little too much enthusiasm, sending Madison Square Garden's stock to the brink of a new 52-week high despite the fact that the season will only be 66 games long rather than the normal 82, resulting in a big hit to the season's revenue. The end of the lockout is cause for celebration, but I find little room for future price appreciation with the stock valued at 22 times forward earnings -- a level that is higher than all but two of its peers and the industry average P/E of 14 . Buying into Madison Square Garden at these levels is likely to end in a brick shot.

Foolish roundup
This week it's all about maintaining a reasonable valuation relative to a sector. Nicor's lack of growth, Aspen's absence of a profit, and Madison's reduction in revenue are enough for me to recommend giving them the old heave-ho! Perhaps you'll follow my lead as I give these three the thumbs-down in my CAPS account; or maybe you feel otherwise?

What's your take on these stocks? Are they sells or belles? Share your thoughts in the comments section below and consider adding Nicor, Aspen Technology, and Madison Square Garden to your free and personalized watchlist to keep up on the latest news with each company.