The $74 million Virtus Small-Cap Sustainable Growth Fund ( PSGAX) is a surprise on the top-performer list, given that small-cap stocks are out of favor after a strong run-up over the past two years. But the fund has a 15.5% return this year, including 9% over the past three months. Its top holding is Hittite Microwave ( HITT), at 6.4% of the portfolio. Its shares are down 4% this year. The company makes integrated circuits, modules and components for radio-frequency and microwave applications. FLIR Systems ( FLIR) is 5% of the fund and has a 10.7% return this year. It makes thermal-imaging and infrared-camera equipment for military, law enforcement and commercial applications. LoopNet ( LOOP), at 5.3% of the fund, is up 66% this year. It operates an online marketplace called LoopNet.com, which is used to match commercial real estate sellers with buyers and landlords with tenants. The company is expected to merge with rival CoStar ( CSGP) late this year, via CoStar's $900 million acquisition of LoopNet.